Modelling issues associated with the synthesis of process operations on a plant-wide scale are discussed, and a hierarchical, distributed, object-oriented modelling framework described. The modelling approach is gener...
Modelling issues associated with the synthesis of process operations on a plant-wide scale are discussed, and a hierarchical, distributed, object-oriented modelling framework described. The modelling approach is generic, and is demonstrated to be suitable for computer-automation of the synthesis of operating procedures. In Part II, provably correct and complete nonlinear planning algorithms based on these models are presented. It is shown that domain-independent planning methodologies using the functional operators required for the synthesis of operating procedures are computationally intractable. Consequently, domain-specific knowledge is exploited within the modelling structure presented in this paper in order to define a tractable methodology for nonlinear planning of process operations. In this paper, we have discussed some of the issues involved in automating the synthesis of plant-wide operating procedures for continuous chemical process. In particular, we have focussed on the question of how to effectively model, on the computer, knowledge about the operation of chemical plants. Previous attempts at modelling have either relied on the restrictive operator- based modelling paradigm, or have employed extremely simplified or situation-specific models. A modelling technique based on a functional operator structure was also considered. This representation accounted for the fact that the outcome of applying an operator is dependent upon the state of the system before execution, and was shown to reduce to the conditional action scheme investigated by researchers in artificial intelligence. Planning with conditional operators involves a plan generation step which is NP-hard, and is therefore considered to be computationally intractable. This justifies the adoption of a domain-specific approach to the planning of process operations, and explains why no algorithmic solution has yet been developed. Realizing the limitations of the operator model, a hierarchical, distrib
The increasing complexity of chemical plants have caused the chemical industry to look towards automated and structured approaches for identifying and diagnosing process abnormalities during the normal course of a pla...
The increasing complexity of chemical plants have caused the chemical industry to look towards automated and structured approaches for identifying and diagnosing process abnormalities during the normal course of a plant's daily operation. One such approach is to make use of a knowledge-based expert system which can perform diagnostic analysis. Many of the recent attempts have focused on using compiled process knowledge, relating symptoms to causes represented as production rules in the knowledge base. Though this leads to real-time diagnostic efficiency, such expert systems lack flexibility to process changes and are incapable of diagnosing novel symptom combinations. The rule-based approaches also lead to knowledge bases that are difficult to develop and maintain as they lack structures that reflect higher-level organization of process knowledge. In this paper, we present a diagnostic methodology that provides the means to solve these problems. We advocate a diagnostic methodology that integrates compiled knowledge with deep-level knowledge, thus achieving diagnostic efficiency without sacrificing flexibility and reliability under novel circumstances. To formalize such an integration, we also propose an object-oriented two-tier knowledge base that houses process-specific compiled knowledge in the top-tier and process-general deep-level knowledge in the bottom-tier. The diagnostic reasoning effectively alternates between the two-tiers of knowledge for efficient and complete diagnosis. An important aspect of diagnostic reasoning is to be able to generate potential causes of the observed symptoms or faults as candidate malfunction hypotheses. We describe an agenda-based inference control algorithm that generates malfunction hypotheses by deriving them from structural and functional information of the process. We discuss the salient features of an expert system, called MODEX2, that has been implemented using these ideas.
The O(M) system is aimed at formalizing reasoning with approximate relations among quantities—relations like “much smaller than” or “slightly larger than.” O(M) is based on seven primitive relations among quantit...
The O(M) system is aimed at formalizing reasoning with approximate relations among quantities—relations like “much smaller than” or “slightly larger than.” O(M) is based on seven primitive relations among quantities, and compound relations formed as implicit disjunctions of consecutive primitives. In the interpretation of the relations, strict interpretation allows exact conservative inferences, while heuristic interpretation allows inferences more aggressive and human-like, by permitting some slack at each inference step. Inference strategies within O(M) are based on propagation of order-of-magnitude relations through properties of the relations, solved or unsolved algebraic constraints and rules. Assumption-based truth-maintenance is used, and the physical dimensions of quantities efficiently constrain the inferences. Statement of goals allows more effective employment of the constraints and focuses the system's opportunistic forward reasoning. O(M) relations permit order-of-magnitude analysis in processengineering. The O(M) system is suitable for many processengineering activities, such as preliminary design of process flowsheets, planning of process operations, design of control structures for chemical plants, fault simulation and diagnosis, process trend analysis and analysis of biochemical pathways.
Gas flow velocity distribution was studied on 1:10 scale cold models of the tops of blast furnaces of three types with particular reference to wear of bell type charging gear. The results, together with observations o...
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Gas flow velocity distribution was studied on 1:10 scale cold models of the tops of blast furnaces of three types with particular reference to wear of bell type charging gear. The results, together with observations on actual blast furnaces, showed that the wear resistance of charging gear is considerably affected by furnace top aerodynamics. Eddy zones were found in the gas offtake region that promote settling of particles on the contact surface and thus reduce charging gear service life.
The paper concerns the development of a laboratory environment suitable to show the fundamental robot control techniques. In the first part the main characteristics of the used robot are detailed together with the con...
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The paper concerns the development of a laboratory environment suitable to show the fundamental robot control techniques. In the first part the main characteristics of the used robot are detailed together with the control electronics. In the second part the C and assembly language software environment is described, which derives from another one developed for research purposes using an IBM XT286 configuration. The interactive software frame, available under either the MS-DOS or the UNIX like QNX operating systems, uses selectable operational modes to analize the performances of different control algorithms. New control algorithms can be developed in C language and installed in the software frame after being off-line tested.
Monitoring of the vapor phase has emerged as a very convenient method for detecting volatile organic contaminants in the subsurface. It can provide a reliable way of placing ground water monitoring and recovery wells....
Monitoring of the vapor phase has emerged as a very convenient method for detecting volatile organic contaminants in the subsurface. It can provide a reliable way of placing ground water monitoring and recovery wells. The most common method uses a driveable ground probe (DGP) to extract a vapor-phase sample followed by direct injection of the vapor into a portable gas chromatograph (GC). However, many regional offices of regulatory agencies and consultants do not have ready access to such equipment. This research explores an alternative–the carbon adsorption method—in which the vapor is withdrawn by the DGP but concentrated on a small activated carbon trap (150mg). The carbon traps can be returned to a central laboratory for solvent extraction and GC analysis. This provides the advantages of increased sensitivity, reduction in field equipment and convenience of in-lab analyses (multiple GC injections are possible). A simple DGP and carbon trap system was constructed and tested at a field site. Vapor-phase concentrations of target compounds present in gasoline were mapped quite conveniently, ranging from 10,000μg/liter (vapor phase) to less than 10μg/L. These concentrations were also shown to decrease in the direction of the ground surface, as expected. Measurements of target compounds in soil showed that the vapor phase contributed a large fraction of the total contaminant burden where a non-aqueous-phase layer (NAPL) had been identified; as important, however, is the rather uniform contamination of the soil outside the NAPL region. Finally, the concentrations of target compounds in the vapor phase and ground water could be related in a manner roughly described by a simple equilibrium model, although exceptions were noted.
A computer model is being developed by the David Taylor Research Center (DTRC) to analyze the tolerance of surface ship combat systems to combat-induced and self-inflicted damage. The work is being done in support of ...
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A computer model is being developed by the David Taylor Research Center (DTRC) to analyze the tolerance of surface ship combat systems to combat-induced and self-inflicted damage. The work is being done in support of the Navy's hull, mechanical and electrical design effort to improve the survivability of surface ship combat systems. The DDG-51 Detailed Design Specifications (Section 072f) and the General Specifications for Ships of the U.S. Navy (1986 Section 072e) both require that damage tolerance analyses be performed. A damage tolerance analysis shows the effect of damage on vital auxiliary and electrical systems and relates these damage effects to the capability of the ship to continue performing its combat mission at a prescribed level. Designated the Computer Aided Design of Survivable Distributed systems (CADSDiS) model, DTRC's deterministic analytical tool consists of portable software to be used by personnel at the activity responsible for the ship design. The model's graphics electrical module is now operating on Digital Equipment Corporation VAX computers at several Navy and commercial activities. Because CADSDiS is highly interactive, it becomes an integral part of the design cycle; this is its major benefit. Thus, damage tolerance analysis information is available to personnel designing the ship within hours or days rather than weeks or months. This computer model will help ensure that the survivability principles of separation and redundancy are incorporated into ship design and are realized in the ship as built.
A nonlinear dynamic model of the Czochralski process, valid throughout the batch growth cycle is derived for use in designing an improved processcontroller. The model is a lumped element representation of the major s...
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A nonlinear dynamic model of the Czochralski process, valid throughout the batch growth cycle is derived for use in designing an improved processcontroller. The model is a lumped element representation of the major system components, and simulates the dynamic system response to disturbances and system inputs. The linearized model is used to determine the system eigenstructure, revealing the system stability, transient response constants, and coupling. Significant results for control design include the identification of the basic time varying nature of the eigenstructure and the disturbances acting on the system, and identification of mechanisms that affect the transient system characteristics. In addition, the growth dynamic effects of liquid encapsulation, low thermal gradient schemes, and magnetic fields are discussed.
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