Real Operating System Research Articles

Simulation and validation of a VAV system with an ANN fan model and a non-linear VAV box model

The results of modelling and simulating a laboratory variable air volume (VAV) test rig are presented. The modelling for each component, such as fan, duct and VAV terminal box, with their control systems, in the test rig has been achieved and the simulations via the logical connection of the component models have been performed by means of an HVACSIM+ platform. A polynomial curve fitting method and a ten neuron sigmoid artificial neural network (ANN) model are used to model the non-linear characteristic of the fan. The ANN is shown to be superior. A non-linear characteristic terminal box model based on the experimental modelling of a European box is developed. The ANN fan model and the terminal box model are inserted in the program of the HVACSIM+ platform as the new component subroutine. The accurate simulation results for the VAV test rig via HVACSIM+ are validated by the real system operation performance.

The maximum coefficient of performance of a two-stage combined heat pump system affected by multi-irreversibilities

SYNOPSIS A general cycle model which includes the multi- irreversibilities often existing in real heat pump systems is established and used to analyse the influence of the irreversibility of finite-rate heat transfer across finite temperature differences, the heat leak between the external heat reservoirs, and the internal dissipation of the working fluid on the performance of a two-stage combined heat pump system. The coefficient of performance is taken as an objective function for optimisation. The maximum coefficient of performance with non-zero specific heating load is determined and other corresponding performance parameters, such as the specific heating load, temperatures of the working fluid in the isothermal processes, the optimal distribution of the heat transfer areas of heat exchangers, and the power input of the heat pump system, are calculated. The results obtained here are more general than those obtained from a two-stage endoreversible combined heat pump system and can guide the optimal design and operation of real combined heat pump systems.

An open source laboratory for operating systems projects

Typical undergraduate operating systems projects use services provided by an operating system via system calls or develop code in a simulated operating system. With the increasing popularity of operating systems with open source code such as Linux, there are untapped possibilities for operating systems projects to modify real operating system code. We present the hardware and software configuration of an open source laboratory that promises to provide students that use it with a better understanding of operating system internals than is typically gained in a traditional operating systems course. Our preliminary projects and evaluation suggest that thus far the lab has achieved its primary goal in that students that used the lab feel more knowledgeable in operating systems and more confident in their ability to write and modify operating system code.

A real bottom-up operating systems course

The "Operating Systems" course is included in the Computer Science undergraduate program of almost all universities. It is quite surprising, however, that teachers rarely agree on what should be taught in such courses. Actually, there even isn't a widely agreed definition of what an operating system is.One of the broadest definitions we ever seen has been given in [2]: The operating system is the collection of functions which make available computing services to people who require them. Therefore, the operating system must fill the gap between the computer and the services required by the people using it. However, what kind of services should we consider? Isn't writing a document with a word processor a computing service that people require? And what about playing a strategy game, or browsing the Web?Much more restricted definitions of operating system have been given. For example, in [6] we read: The purpose of an operating system is to provide an environment in which a user can execute programs. The primary goal of an operating system is thus to make the computer system convenient to use. A secondary goal is to use the computer hardware in an efficient manner. Most Operating Systems courses implicitly adopt this definition or a similar one, because it allows teachers to stick to a well-defined set of canonical topics. Actually, two kinds of operating systems courses may co-exist: one addressed to system administrators and one to system programmers. In the first case, the course should teach how to make use of the many existing features inside an OS, how to tune it up properly, and how to set up proper environments for the users. In the second case, the course should explain how the functions are implemented and which are the main issues and trade-offs to be considered while implementing them.In fact, the first kind of course is seldom included in an undergraduate Computer Science program: this is likely due to the fact that operating systems are quite different from each other, thus the experience gathered on one of them, say Sun Microsystem's Solaris, cannot be readily transfered to another one, say IBM's OS/390. We thus concentrate in the rest of this paper on the second type of course, the standard elective fourth year course of an Undergraduate program in Computer Science.

Simulation of a computer-controlled dehydrator

Experimental data that can be obtained during investigation of a real system in operation, under different working conditions and different input parameters (combined with different control parameters), are usually not sufficient. Unsuitable working conditions can cause losses during production (which cannot be afforded), while some of the input parameters (like moisture content of the input material) are not under the control of the investigator. A suitable way to avoid this problem is to use a simulation program in order to explore different regimes and to obtain the optimal one. Investigations can be carried out using simulation programs in order to ascertain the influence of different control parameters on the behavior of the entire system, and to obtain control parameters that give the smallest deviations of a certain variable from the nominal value. It is also possible to obtain the values of control parameters causing nonstability of the system. The developed simulation program for the control system of a dehydrator includes a model of the drying process, a model describing the behavior of different functional blocks of the dehydrator (including the inertia of the system), simulation of the control of drying agent temperature at the dryer exit as a function of the fuel flow rate, and simulation of the fuel consumption as well as the dried material production.

The enhanced data acquisition system for the 4/spl pi/ detector CHIMERA

CHIMERA is a second generation 4/spl pi/ detector for high resolution light particle and fragment measurements in the field of intermediate energy nuclear reactions. An enhanced data acquisition, control and trigger system has been developed to manage the almost 5000 electronic channels of the detector. The data acquisition system is based on a Fast Data Link (FDL) connection between 9U VME crates. The FDL is a highly programmable VME device. It performs data readout and transfer to a destination VME CPU, the FIC8243, running the real time OS9 operating system. Data read and transfer is performed by a fast protocol (Sparse Data Scan) whose performances have been improved introducing the Chained Block Transfer mode (CBLT) technique. Data collected by the CPU are broadcast to analysis work-stations for on-line data analysis and storage. All commands from and to the VME CPU are sent by socket-based network protocols. Complete remote control of the electronic front-end is obtained by a system of client-server applications. A first level event selection and control during readout is made by a trigger system based on a new VME 9U board (MUSE), fully integrated with the FDL readout system.

Emergence and erosion: a model for rill initiation and development

Soil erosion by overland flow, resulting from infiltration-excess rainfall, generates rill networks on hillslope areas. The way in which these networks emerge and develop suggests that hillslope erosion functions as a self-organizing dynamic system. Based upon this argument, a model for soil erosion (RillGrow 1) has been developed: this operates at the spatial scale of raindrops and microtopography. In this paper the second generation of the model (RillGrow 2) is described and applied to four different soil surfaces. Results suggest that, even at this early stage in its development, RillGrow 2 is capable of replicating the success of the earlier model and in some cases of extending them. The success of both models suggests that this self-organizing view of rill generation may capture some fundamental aspects of the operation of real erosional systems. Copyright © 2000 John Wiley & Sons, Ltd.

Performance characteristics of a two-stage irreversible combined refrigeration system at maximum coefficient of performance

A general cycle model of a two-stage combined refrigeration system is established and used for analizing the influence of multi-irreversibilities, such as finite rate heat transfer, heat leak between the heat reservoirs and internal dissipation of the working fluid, on the performance of the refrigeration system. The coefficient of performance is taken as an objective function for optimization. The maximum coefficient of performance is calculated, and other corresponding performance parameters, such as the temperatures of the working fluid in the isothermal processes, the optimal distribution of the heat transfer areas and the power input of the refrigeration system, are determined. The results obtained here are more general than those obtained from a two-stage endoreversible combined refrigeration system and can guide the optimal design and operation of real combined refrigerator systems.

Le centre des mouvements de l'eau (CME), simulateur du comportement hydraulique et qualité du réseau du Syndicat des Eaux d'Ile de France

The Centre des Mouvements de l'Eau (CME), operational since 1991 is a centralized Supervisory Control And Data Acquisition (SCADA) system for the water production and distribution network of the Syndicat des Eaux d'Ile de France (SEDIF) which serves approximately 4,000,000 inhabitants around Paris (France). In 1994, the SEDIF and its operator, Generale des Eaux (VIVENDI group) initiated a project called the 'CME-phase II' project with the aim of linking the CME SCADA system with a network analysis software (the Stoner Workstation Service) capable of simulating the hydraulic and water quality operation of the water network. This application is operational since 1997 and provides the SEDIF with a new set of tools to better supervise the operation of the network, predict potential problems in the network and validate different operational strategies. On-line simulations (i.e. in parallel to the real system operation) allows for anomaly detection and resolution: a new set of operational data is received from the SCADA system at a predefined time interval and is used to update the hydraulic model before executing a steady state simulation. Key points in the network can be closely controlled (without supplementary monitoring equipment) and potential discrepancies between calculated and observed data can be detected and analyzed. The entire process is fully automatic and does not require any operator intervention. Off-line past simulations allow the operator to replay an event that took place in the network using the operational data archived by the SCADA system with the objective of better understanding the hydraulic and water quality behavior of the network. Off-line predictive simu1ulations allow the operator to test various operational strategies. Using as a starting point the newest set of operational data and defining the network demand and the facilities operation in the coming hours or days, the operator can initiate a variable simulation and assess the consequences of a specific operational strategy. The CME phase II application is also extensively used to validate any extension or reinforcement project as it permits a quick extraction and validation of SCADA data to calibrate a hydraulic model before assessing the impact of a new extension or reinforcement scheme.

Single Sample Path-Based Optimization of Markov Chains

Motivated by the needs of on-line optimization of real-world engineering systems, we studied single sample path-based algorithms for Markov decision problems (MDP). The sample path used in the algorithms can be obtained by observing the operation of a real system. We give a simple example to explain the advantages of the sample path-based approach over the traditional computation-based approach: matrix inversion is not required; some transition probabilities do not have to be known; it may save storage space; and it gives the flexibility of iterating the actions for a subset of the state space in each iteration. The effect of the estimation errors and the convergence property of the sample path-based approach are studied. Finally, we propose a fast algorithm, which updates the policy whenever the system reaches a particular set of states and prove that the algorithm converges to the true optimal policy with probability one under some conditions. The sample path-based approach may have important applications to the design and management of engineering systems, such as high speed communication networks.

Dealing with time

Maps are involved as soon as one decides to understand spatial relationships and patterns. Most maps limit themselves to a single snapshot in time. However, the study of geographical processes cannot be successful without considering time as well, because these events only happen as time passes. When maps have to depict events, an inventive design approach is required to keep them clear and understandable. A classic example is the Minard map from 1861 showing Napoleon's ad ventures in Russia (Robinson 1967). Maps displaying events that stretch over time tend to become rather complex. The solution is to split the master map into a set of maps to be read as a comic. The maps in the set are less cluttered, but the reader needs greater skills to combine the information they provide into a event, especially when that event is a process (Kousoulakou and Kraak 1992). With advancing technology, animation seems to be the solution. To understand the process represented by animation the viewer should have interface tools available, for instance, to go back and forward, pause and stop. Without these tools the animation is even more limited then the set of maps where the reader has freedom to move from one image to another to retrieve information. Considerable (cartographic) research has been done on the application of animation to display time (DiBiase et al. 1992; Peterson 1995; Ormeling 1996; Dransch 1997). The new cartographic techniques do not stand isolated. Their development and use is an integral process of the spatial data handling process. We need an understanding of concepts and techniques to acquire the necessary data and model them, and we need powerful computer environments to structure and store the data (Snodgrass 1992; Jensen et al. 1994). We also need techniques to query and retrieve the data for further understanding and display (Kraak and MacEachren 1996) (see Figure 1). [FIGURE 1 OMITTED] Where do we stand? Despite the current advanced state of the art of geographic information systems (GIS) we still have only limited capabilities to model and manipulate temporal data, especially if we do not want to limit ourselves to the study of snapshots. Time in relation to geography has been a subject of study for some time now. In the sixties, the approach to time became more structured (Hagerstrand 1967). With respect to GIS, the serious study of time started at the beginning of the nineties with Langran's Time in Geographic Information Systems (1993). How far have we come since then? While a number of systems such as Tempest are under study (Peuquet 1994), and contrary to vendors' claims, real operational systems are still unavailable. Time is a complex topic; it is not tangible, and it is perceived and measured accordingly. One of the major problems is the understanding of its use in daily geo-life. The NCGIA's Initiative 10 on spatio-temporal reasoning in GIS and related activities in research attempted to tackle this problem, with the effort resulting in an interesting book edited by Egenhofer and Gollege (1998). However, the final words have not yet been said. This issue of Cartography and Geographical Information Science is an initiative of the International Cartographic Association's Commission on Visualization. It covers most aspects of the spatial data handling process related to time. The contributors share an interest in investigating the term but each contributor looks at movement from a different perspective. Not only do the particular phases of the spatial data handling process influence the view on movement, but so does also the background of the authors or the problems they try to solve. The different perspectives might confuse the reader because of the difference in terminology used when the focus is on pure geography or database building, or when the process of spatial data handling is described by a cartographer or a computer scientist. …

The real time plasma control system of Tore Supra

The Tore-Supra real time plasma control system, operational since 1988, was completely redesigned in 1995 with VME hardware and PowerPC processors monitored by a real time UNIX operating system (LynxOS™). Now, with five units interconnected through a fast shared memory network, a global plasma control has been built. Plasma current, shape, and gas control are already established and it is expected that control of the plasma current profile will be achieved before the end of 1997. The introduction of a specific unit with a graphic man-machine interface in the shared memory network is under development which will allow interactive verification of parameters. This new architecture is flexible and open-ended. It will enable interconnection to other Tore Supra systems such as those required for the long-term programme of long pulse (1000s) discharges.

The coefficient of performance of a multi-temperature-level absorption heat transformer at maximum specific heating load

An endoreversible cycle model of a multi-temperature-level absorption heat transformer is set up and used to analyse the performance of the heat transformer affected by the irreversibility of finite-rate heat transfer. The key performance parameters, such as the coefficient of performance, specific heating load, temperatures of the working fluid in the heat exchangers, heat-transfer areas of the heat exchangers and so on, are optimized. Some new results which are conducive to the optimal design and operation of real heat transformer systems are obtained and several special cases are discussed in detail. Moreover, the endoreversible cycle model is generalized to become an irreversible cycle model. The important results describing the optimal performance of a multi-temperature-level absorption heat transformer affected simultaneously by the internal and external irreversibilities can be obtained simply and conveniently from the corresponding formulae of the endoreversible cycle model because of the introduction both of the equivalent temperatures and of the equivalent overall heat-transfer coefficients.

A framework for modelling and simulating data flows in distributed computing systems

This paper introduces a framework for modelling and simulating the behaviour of distributed computing systems. The framework comprises both means for abstract modelling and an implementation that allows the evaluation of abstract models by means of discrete event simulation. The basic characteristics of distributed computing systems used for physics data processing at CERN are presented, motivating the purpose and need for modelling and simulation. As an example, the central data recording system of a current High-Energy Physics experiment is introduced. The modelling framework provides concepts to structure relevant state information of a system; The most important factor to set up the structure of components encapsulating state information is thereby given by dynamic aspects of the system, i.e. by identified data flows. Traditional approaches to modelling often tend to focus purely on static, architectural system aspects. All abstract concepts are motivated and demonstrated using an example. Results of the simulation are compared to figures measured during real system operation, rating the proposed framework and its underlying modelling approach.

System calls and interrupt vectors in an operating systems course

The introductory operating systems course has a tendency to appear to the student as a disparate collection of topics such as synchronization primitives, process scheduling algorithms, and page replacement policies. We describe a sequence of material to cover early in the operating systems course that prevents this tendency by clarifying the goal of the course and by providing a framework for understanding how the later course material is used in kernel design. The material centers around two concepts. First is the importance of the abstraction provided by the system call interface, that the kernel is the implementation of that interface, and the analogy with the instruction set interface the student has already encountered. Second is how the interrupt vector mechanism in a broad sense is central to how the kernel functions and underpins the actual implementation of many of the other topics in the course. Illustration through code from a real operating system kernel is a key feature of how this sequence makes clear the workings of an operating system.

Automated control system for HgI/sub 2/ crystals growth

The authors describe the control system developed for the automated growth of HgI{sub 2} crystals, mainly used for X and {gamma} radiation detectors. The system includes instrumentation for the precise measurement of the growth furnace temperatures and for their control, both needed to fulfill the strict requirements of the vapor phase crystal growth. A video camera and a VME grabber module allow the detection of the crystal nucleation and pattern recognition. This image analysis is used as input for the control actions. A VME based computer (MVM147SA-1 from Motorola) running a real time OS9 operating system performs: data collection, instrumentation programming, image acquisition, data analysis and control of the whole system making use of a highly structured software. The image analysis is done by means of a perceptron neural net classifier using a parameter invariant representation of the objects detected in the segmented images.

Optimal load‐shedding using local information

AbstractThis paper describes an optimal load‐shedding policy based on quadratic programming using only some power system state variables after severe generation outages. When generation outage is severe, the imbalance between supply and demand causes a declining frequency. Utilities generators cannot be operated excessively at frequencies above normal. Some of the load must be shed to prevent system damage. Optimal load‐shedding policies have been studied using all state variables of the power system. However, in real power system operations, it is difficult to obtain remote information in that fraction of a second following generation outages.An optimal load‐shedding method is constructed in this research using quadratic programming (QP) under the assumption that all power system state variables can be available. However, these state variables cannot be easily accessible (as already mentioned). A suboptimal load‐shedding scheme based on the local state variables is then studied. The proposed load‐shedding method is based on the aforementioned optimal one. The change in line‐power flows and the amount of generation power outage are used as accessible data at each load point. Incorporating this local information into the optimal loadshedding method based on the QP method, the proposed load‐shedding method is established here.The effectiveness of this proposed method is illustrated by two examples and simulation results on a model power system show that the method is encouraging.

Load balancing and fault tolerance in workstation clusters migrating groups of communicating processes

In the past, several process migration facilities for distributed systems have been developed. Due to the complex nature of the subject, all those facilities have limitations that make them usable for only limited classes of applications and environments. We discuss some of the usual limitations and possible solutions. Specifically, we focus on migration of groups of collaborating processes between Unix systems without kernel modifications, and from this we derive the design for a migration system. First experiences with our implementation show that we reach performance figures for the migration that are close to those of real distributed operating system.

Supervision of Annealing Furnaces

Objective: To implement a monitoring and supervision system for the annealing plant number one at SIDERAR (66 bases and 25 furnaces) allowing product analysis, technological tracking and data processing. The key point of this work is to guarantee the heating process is done according to the preprogrammed curves.Methods: The system will be running on a multitasking real time microkernel operating system and the application will be programmed in C language. It will allow the process analysis of each base, alarm and product databases and report generation. The whole system consists of a hot standby configuration allowing fast recoveries from shutdown nodes. The control unit is a Taylor MOD-30 whose setpoints are calculated by the PC level. The variable under control and the heating curve is product dependent. Event handling procedures allow the detection of abnormal situation and correction in real time.Conclusion: The system will keep a reliable amount of information for the technological tracking thus increasing the product quality. Efficiency factors will be then calculated allowing reduction of dead times. Event storage will let error tracking analysis although the product has already been finished.

Real-time data management in a flexible manufacturing system (FMS)

The need for more flexible and efficient data management in manufacturing systems has become obvious. To secure the highest utilization rate and maximum productivity of manufacturing systems, it is necessary to be able to find the right information at the right time and at the right place: Just In Time. Non production and inefficiency in single operated, stand-along NC-machine tools and other NC-equipment are due largely to humanly caused elapsed times between the receipt of information, the formulation of a decision and the performance of the command. The advantages of Flexible Manufacturing systems (FMS) are obvious if they are compared to stand-along machines. FMS-concepts, hardware and software-state of the art, are designed mostly on the idea of centralized control. These types of systems are difficult and expensive to expand and maintain. Centralization makes the FMS dependent on a network and a main computer that might cause troubles with breakdowns. This paper presents solutions for decentralization and real-time data management of the control system of an FMS. An FMS has to be capable of controlling its resources and its state in real-time and take care of the connections to upper levels of enterprise network (CIM). This leads to the use of real time multi-tasking operating systems and suitable software for system developing. Relational Database Management systems (RDBMS) are very common in administrative use but in process-control information management solutions are still based on traditional ways of programming. Standard RDBMSs offer an easier way to integrate the manufacturing information system with other computer aided (CA-) subsystems through Local Area Networks (LANs). Dependency on the format in which the data is stored is not so crucial if the strategic decision of the company-wide standard for data management has been approved. The most useful approach to factory systems integration is the modularity of flexible components that are to be implemented to the system. Only in this way it is possible to design systems that are flexible and expandable also in the future. When the system is implemented the technology is at the certain level and the requirements for the products made in the system are well known. In the future, demands to expand the system with new facilities might become topical. If there is already a modular system it is not a great problem to install new equiptment in the system.