No description available.

The work presented herein describes the production of hot strip with special attention to the runout table. Because of its high capital and operating costs, a new principle in conveying the strip using an air cushion and a new cooling system for strip cooling have been proposed. Information given here is nearly all from available literature and the author's own experience with Hot Strip Mill production problems. To support the idea of using an air cushion for strip conveying, experimental equipment was designed and built which confirmed the feasibility of the method. A new cooling system was also proposed to meet the ever increasing requirements for better mechanical properties of hot strip. Runout table design application may serve as a guideline in designing new Hot Strip Mill runout table. / Thesis / Master of Engineering (ME)

Rolling technology can control the thickness precisely. But it isn¡¦t available in width control. FEM software DEFORM 3D is adopted to simulate one stand of the hot finishing rolling process using carbon steel as sheet material. Stress, strain and width spread are discussed. Regression analysis is used to find an empirical equation for rolling load and width spread. Experiment and simulation of cold strip rolling using aluminum as sheet material are conducted,discussing the width spread and detail of width transformation in DEFORM 3D.From the comparisons between analytical and experimental width spread, the analytical model and prediction equation are validated.

Recently, the accuracy of hot strip gage is strictly demanded, and the strip thickness becomes the most important quality in hot strip rolling. It is well known that the accuracy of final strip thickness in the hot strip mill depends on the gage control performance at each stand. In order to improve the quality of the hot strip gage and reduce the strip thickness deviation , the Automatic Gage Control(A.G.C) system now is widely used in modern hot strip mills of the world. In this paper, the principle of feedforward control strategy in the AGC system is discussed and it¡¦s control performance is deeply analyzed. Besides, based on the study of comprehensively mathematical model and the establishment of simulator, the mathematical analysis and the simulation result can clarify the influence of the control system on strip thickness.

Hot-rolled steel products occupy a key position, between upstream and downstream, in the steel industry chain. In this country, revenue of hot-rolled strip steel products maintains the greatest proportion among all steel products. Continuous pursuit of knowledge progress and growth plays a significant support to sustainable enterprises and gives them a vigorous operational strength in the face of international competition. During the hot strip steel manufacturing process, as the second-level standard of the computer integrated manufacturing system in a steel plant describes, in addition to those needed information related with real-time electronic control equipment dealt by process control computers, how does hot strip mill statistical process computer, abbreviated HSMSPC, utilize statistical analysis and information processing also challenges the future competitiveness. This research engages in a genuine hot strip mill statistical process computer system developed by a well-known steel corporation located in Taiwan, adopting structure behavior coalescence, abbreviated as SBC, six golden rules to build up the architecture-oriented hot strip mill statistical process computer model, abbreviated as AOHSMSPCM. AOHSMSPCM shall construct a hot strip mill statistical process computer system in an architecture-oriented way so that it is able to fully express the operational act and information extraction which cover system structures and system behaviors as well; subsequently, the hot strip mill statistical process computer system will produce higher added value in the face of the production line variability, replicate update, knowledge management, and so on. AOHSMSPCM begins with the analysis layer of system architecture. In this research, system structures and system behaviors are well described in the HSMSPC analysis layer. Besides this, easy to duplicate and extension of scalability are thoroughly elaborated in this research. Finally, this research comes up with "Strengthening the variability control of a hot strip mill", "Preserving assets of corporate knowledge" and "Upgrading process technologies of production lines" as three benefits that AOHSMSPCM contributes to the enterprise.

Abstract In today's world, enormous amounts of data are being collected everyday. Thus, the problems of storing, handling, and utilizing the data are faced constantly. As the human mind itself can no longer interpret the vast datasets, methods for extracting useful and novel information from the data are needed and developed. These methods are collectively called knowledge discovery methods. In this thesis, a novel combination of feature selection and data modeling methods is presented in order to help with this task. This combination includes the methods of basic statistical analysis, linear correlation, self-organizing map, parallel coordinates, and k-means clustering. The presented method can be used, first, to select the most relevant features from even hundreds of them and, then, to model the complex inter-correlations within the selected ones. The capability to handle hundreds of features opens up the possibility to study more extensive processes instead of just looking at smaller parts of them. The results of k-nearest-neighbors study show that the presented feature selection procedure is valid and appropriate. A second advantage of the presented method is the possibility to use thousands of samples. Whereas the current rules of selecting appropriate limits for utilizing the methods are theoretically proved only for small sample sizes, especially in the case of linear correlation, this thesis gives the guidelines for feature selection with thousands of samples. A third positive aspect is the nature of the results: given that the outcome of the method is a set of conditional probabilities, the derived model is highly unrestrictive and rather easy to interpret. In order to test the presented method in practice, it was applied to study two different cases of steel manufacturing with hot strip rolling. In the first case, the conditional probabilities for different types of retentions were derived and, in the second case, the rolling conditions for the occurrence of wedge were revealed. The results of both of these studies show that steel manufacturing processes are indeed very complex and highly dependent on the various stages of the manufacturing. This was further confirmed by the fact that with studies of k-nearest-neighbors and C4.5, it was impossible to derive useful models concerning the datasets as a whole. It is believed that the reason for this lies in the nature of these two methods, meaning that they are unable to grasp such manifold inter-correlations in the data. On the contrary, the presented method of conditional probabilities allowed new knowledge to be gained of the studied processes, which will help to better understand these processes and to enhance them.

No description available.

No description available.

This dissertation is devoted to the development of new flow-based formulations for the asymmetric traveling salesman problem (ATSP) and to the demonstration of their applicability in effectively solving some scheduling problems. The ATSP is commonly encountered in the areas of manufacturing planning and scheduling, and transportation logistics. The integration of decisions pertaining to production and shipping, in the supply chain context, has given rise to an additional and practical relevance to this problem especially in situations involving sequence-dependent setups and routing of vehicles. Our objective is to develop new ATSP formulations so that algorithms can be built by taking advantage of their relaxations (of integer variables, thereby, resulting in linear programs) to effectively solve large-size problems. In view of our objective, it is essential to have a formulation that is amenable to the development of an effective solution procedure for the underlying problem. One characteristic of a formulation that is helpful in this regard is its tightness. The tightness of a formulation usually refers to the quality of its approximation to the convex hull of integer feasible solutions. Another characteristic is its compactness. The compactness of a formulation is measured by the number of variables and constraints that are used to formulate a given problem. Our formulations for the ATSP and the scheduling problems that we address are both tight and compact. We present a new class of polynomial length formulations for the asymmetric traveling salesman problem (ATSP) by lifting an ordered path-based model using logical restrictions in concert with the Reformulation-Linearization Technique (RLT). We show that a relaxed version of this formulation is equivalent to a flow-based ATSP model, which, in turn, is tighter than the formulation based on the exponential number of Dantzig-Fulkerson-Johnson (DFJ) subtour elimination constraints. The proposed lifting idea is applied to derive a variety of new formulations for the ATSP, and a detailed analysis of these formulations is carried out to show that some of these formulations are the tightest among those presented in the literature. Computational results are presented to exhibit the relative tightness of our formulations and the efficacy of the proposed lifting process.> While the computational results demonstrate the efficacy of employing the proposed theoretical RLT and logical lifting ideas, yet it remains of practical interest to take due advantage of the tightest formulations. The key requirement to accomplish this is the ability to solve the underlying LP relaxations more effectively. One approach, to that end, is to solve these LP relaxations to (near-) optimality by using deflected subgradient methods on Lagrangian dual formulations. We solve the LP relaxation of our tightest formulation, ATSP6, to (near-) optimality by using a deflected subgradient algorithm with average direction strategy (SA_ADS) (see Sherali and Ulular [69]). We also use two nondifferentiable optimization (NDO) methods, namely, the variable target value method (VTVM) presented by Sherali et al. [66] and the trust region target value method (TRTV) presented by Lim and Sherali [46], on the Lagrangian dual formulation of ATSP6. The preliminary results show that the near-optimal values obtained by the VTVM on solving the problem in the canonical format are the closest to the target optimal values. Another approach that we use is to derive a set of strong valid inequalities based on our tighter formulations through a suitable surrogation process for inclusion within the more compact manageable formulations. Our computational results show that, when the dual optimal solution is available, the associated strong valid inequalities generated from our procedure can successfully lift the LP relaxation of a less tight formulation, such as ATSP2R¯, to be as tight as the tightest formulation, such as ATSP6. We extend our new formulations to include precedence constraints in order to enforce a partial order on the sequence of cities to be visited in a tour. The presence of precedence constraints within the ATSP framework is encountered quite often in practice. Examples include: disassembly optimization (see Sarin et al. [62]), and scheduling of wafers/ ICs on automated testing equipments in a semiconductor manufacturing facility (see Chen and Hsia [17]); among others. Our flow-based ATSP formulation can very conveniently capture these precedence constraints. We also present computational results to depict the tightness of our precedence-constrained asymmetric traveling salesman problem (PCATSP) formulations. We, then, apply our formulations to the hot strip rolling scheduling problem, which involves the processing of hot steel slabs, in a pre-specified precedence order, on one or more rollers. The single-roller hot strip rolling scheduling problem can be directly formulated as a PCATSP. We also consider the multiple-roller hot strip rolling scheduling problem. This gives rise to the multiple-asymmetric traveling salesman problem (mATSP). Not many formulations have been presented in the literature for the mATSP, and there are none for the mATSP formulations involving a precedence order among the cities to be visited by the salesmen, which is the case for the multiple-roller hot strip rolling scheduling problem. To begin with, we develop new formulations for the mATSP and show the validity of our formulations, and present computational results to depict their tightness. Then, we extend these mATSP formulations to include a pre-specified, special type of precedence order in which to process the slabs, and designate the resulting formulations as the restricted precedence-constrained multiple-asymmetric traveling salesman problem (rPCmATSP) formulations. We directly formulate the multiple-roller hot strip rolling scheduling problem as a rPCmATSP. Furthermore, we consider the hot strip rolling scheduling problem with slab selection in which not all slabs need to be processed. We model the single-roller hot strip rolling scheduling problem with slab selection as a multiple-asymmetric traveling salesman problem with exactly two traveling salesmen. Similarly, the multiple-roller hot strip rolling scheduling problem with slab selection is modeled as a multiple-asymmetric traveling salesman problem with (m+1) traveling salesmen. A series of computational experiments are conducted to exhibit the effectiveness of our formulations for the solution of hot strip rolling scheduling problems. Furthermore, we develop two mixed-integer programming algorithms to solve our formulations. These are based on Benders΄ decomposition [13] and are designated Benders΄ decomposition and Modified Benders΄ methods. In concert with a special type of precedence order presented in the hot strip rolling scheduling problems, we further introduce an adjustable density ratio of the associated precedence network and we use randomly generated test problems to study the effect of various density ratios in solving these scheduling problems. Our experimentation shows the efficacy of our methods over CPLEX. Finally, we present a compact formulation for the job shop scheduling problem, designated as JSCD (job shop conjunctive-disjunctive) formulation, which is an extension of our ATSP formulations. We use two test problems given in Muth and Thompson [53] to demonstrate the optimal schedule and the lower bound values obtained by solving the LP relaxations of our formulations. However, we observe that the lower bound values obtained by solving the LP relaxations of all variations of our JSCD formulation equal to the maximum total processing time among the jobs in the problem. / Ph. D.

Dans cette thèse, on s'est attaché à résoudre un certain nombre de problèmes qui apparaissent lorsqu'on traite des problèmes concrets de contrôle: phénomènes à plusieurs échelles de temps, discontinuités de la commande lors du basculement d'un correcteur à un autre, nécessité de concevoir un nombre limité de correcteurs différents malgré une gamme très importante des produits traités. Pour illustrer concrètement les résultats obtenus, nous nous sommes appuyés sur un exemple industriel concret, le contrôle de guidage de bande durant le processus de laminage dans un laminoir à chaud. D'abord, nous proposons une solution convexe au problème de commande optimale linéaire quadratique pour les systèmes linéaires à deux échelles de temps en temps discret. Ensuite, nous établissons des conditions suffisantes, formulées sous la forme d'inégalités matricielles linéaires, qui permettent de vérifier la stabilité d'un système à commutation à deux échelles de temps et de synthétiser des correcteurs stabilisants. Nous proposons aussi dans ce travail une méthode pour minimiser les discontinuités sur la commande dans le cadre des systèmes à commutation. Dans le contexte du contrôle de guidage de bande pour un laminoir à chaud, nous ne pouvons pas négliger l'influence des paramètres incertains, qui sont dus principalement au fait que ce genre de système traite une gamme de produits très large. Donc, dans la synthèse du correcteur, nous prenons en compte ces variations en divisant l'ensemble des produits en plusieurs familles et en synthétisant un correcteur différent pour chaque famille / This Ph.D. thesis deals with a certain number of problems arising in practical implementation of control systems: multi time scale phenomena, sudden modifications on the system dynamics, discontinuities on the control signal due to controller switchings, the need of design a limited number of controllers in spite of a wide variation on the physical parameters. In order to illustrate the validity of the obtained results, we resort to a real problem concerning the steel production framework, the robust steering control of a hot strip finishing mill. First, a convex solution of the linear quadratic control design for discrete two time scale systems is proposed. Hence, we address the stability problem of two time scale switched systems. We show that stability of the slow and fast switched subsystems under arbitrary switching rules does not imply the stability of the corresponding two time scale switched system in the singular perturbation form. An additional constraint, independent of the value of the singular parameter and of the switching rule, is provided in terms of linear matrix inequalities. We also introduce a bumpless transfer method for switched systems aiming at reducing the discontinuities on the control signal. Dwell time conditions assessing the asymptotic stability of the closed loop switched system are established. The practical contribution of this thesis, the robust steering control design, exploits most of previous results. The objective is to guarantee the stability of the hot strip mill system and improve the quality of the rolled products