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EN
Although there currently exists a wide range of voltage regulators that are commercially available, the search for devices with a simpler physical design remains the focus of research studies. Following this line, an electromagnetic voltage regulator (EVR) arrangement has been proposed. The EVR is constituted of an autotransformer that supplies, via discrete taps, a series transformer that injects voltage for regulating the feeder voltage. Even though its operating principle is shown as being similar to that of other devices on the market, the physical arrangement and operating strategy of EVR show novelties which result in properties such as: economic attractiveness, constructive simplicity, and operational reliability. Moreover, when installing voltage regulators, efficacy studies must be carried out to optimize equipment design. In this context, this paper aims at evaluating the factors that influence the effectiveness of the EVR in restoring voltage variations according to the determinations imposed by regulatory agencies. The ultimate goal of this study is to determine the voltage deviation range that the EVR is able to restore. To achieve this goal, a mathematical modeling of the EVR is given and study cases are computationally carried out to investigate its performance when connected to a typical distribution feeder.
EN
The successful selection process of industrial robots (IRs) for today’s Cyber-Physical Systems is an important topic and there are different possibilities to solve the task. The primary task is to estimate the existing IR selection systems according to the suitability analysis and to highlight the main positive features and problematic areas. The objective of the reverse task is to carry out the sensitivity analysis of the existing robot-based manufacturing systems. The matching of these two approaches helps decision makers to develop the main principles of IR selection in today’s multidimensional and fast-changing economic world.
EN
International requirements for improving energy efficiency and environmental protection and the necessary goals for their implementation in the marine industry are an actual problem. To integrate state-of-the-industry technologies and marine specialists education, the training complex is proposed. It is based on the platform of a hardware-software complex with the ability to integrate training equipment, simulators and software. That makes such a training complex multitask, universal, and flexible in achieving a variety of tasks and goals. The complex also implements high-quality education and training of marine specialists, conducting research after processing working out the results of engineering modelling of structural, thermal power, hydraulic, electrical, electronic, multi-physical and other solutions. The need to use the training complex allows us to form the necessary competence of the engine team personnel, develop methods and criteria for assessing competence, evaluate and demonstrate practical skills.
PL
Międzynarodowe wymogi dotyczące poprawy efektywności energetycznej i ochrony środowiska oraz cele niezbędne do ich wdrożenia w przemyśle morskim stanowią aktualny problem. W celu zintegrowania najnowocześniejszych technologii i kształcenia specjalistów z branży morskiej proponuje się utworzenie kompleksu szkoleniowego. Jest on oparty na platformie kompleksu sprzętowo-programowego z możliwością integracji sprzętu szkoleniowego, symulatorów i oprogramowania. To sprawia, że taki kompleks jest wielozadaniowy, uniwersalny i elastyczny w realizacji różnorodnych zadań i celów. Ponadto kompleks realizuje wysokiej jakości kształcenie i szkolenie specjalistów morskich, prowadząc badania po opracowaniu wyników modelowania inżynierskiego rozwiązań konstrukcyjnych, cieplnych, hydraulicznych, elektrycznych, elektronicznych, i innych. Wykorzystanie kompleksu szkoleniowego pozwala na kształtowanie niezbędnych kompetencji personelu zespołu inżynierskiego, opracowanie metod i kryteriów oceny kompetencji, ocenę i wykazanie umiejętności praktycznych.
EN
The continuous improvement in the industries and organizations hinges upon the evaluation of their performance. In fact, the performance evaluation assists organizations to identify their strengths and weaknesses and, accordingly, enhance their efficiency. As soon as the concept of sustainability was propounded in the engineering based industries, the performance evaluation got more importance due to the environmental issues and social concerns along with the economical aspects. Therefore, this paper is an attempt to propose an approach based on fuzzy best-worst method (BWM) and fuzzy inference system (FIS) in order to evaluate the performance of an Iranian steel complex in terms of sustainability concept. In the proposed approach, the weights of some selected criteria were determined by fuzzy BWM method and, then, the score of the under study industry was calculated in terms of economic, environmental, and social aspects. At the end, an FIS was developed to calculate the final score of the intended industry. In order to check the efficiency of the proposed approach, its performance was measured using expert knowledge as well as real data of a steel complex in Iran. A moderate to high performance has been achieved for the understudy case through conducting the proposed approach. It was suggested that the industry should focus on the criteria with both high weights and low evaluated scores (for example the environmental management technologies and knowledge criterion) to increase its performance evaluation score. The obtained results were indicative of the efficiency of the proposed approach.
PL
Ciągłe doskonalenie branż i organizacji zależy od oceny ich wydajności. W rzeczywistości ocena wyników pomaga organizacjom zidentyfikować ich mocne i słabe strony, a co za tym idzie, zwiększyć ich efektywność. Jak tylko koncepcja zrównoważonego rozwoju została zaproponowana w branżach opartych na inżynierii, ocena wydajności nabrała większego znaczenia ze względu na kwestie środowiskowe i społeczne, a także aspekty ekonomiczne. Artykuł jest próbą zaproponowania podejścia opartego na rozmytej metodzie best-worst (BWM) i rozmytym systemie wnioskowania (FIS) w celu oceny wydajności irańskiego kompleksu stalowego pod kątem koncepcji zrównoważonego rozwoju. W proponowanym podejściu, wagi wybranych kryteriów wyznaczono metodą rozmytą BWM, a następnie obliczono punktację badanej branży pod względem ekonomicznym, środowiskowym i społecznym. Na koniec opracowano rozmyty system wnioskowania FIS, aby obliczyć końcowy wynik dla planowanej branży. Aby sprawdzić efektywność proponowanego podejścia, mierzono jego wydajność, wykorzystując wiedzę ekspercką oraz rzeczywiste dane dotyczące kompleksu stalowego w Iranie. W analizowanym przypadku, poprzez zastosowanie proponowanego podejścia osiągnięto wyniki od umiarkowanych do wysokich. Zasugerowano, że w celu zwiększenia oceny wyników, branża powinna skupić się na kryteriach zarówno o dużej wadze, jak i nisko ocenianych punktach (na przykład technologie zarządzania środowiskowego i kryterium wiedzy). Uzyskane wyniki świadczyły o skuteczności zaproponowanego podejścia.
PL
Zasadniczy aspekt uczenia maszynowego stanowi ocena jakości zbudowanych modeli. Niezbędne zatem staje się staranne zaplanowanie eksperymentów. Potrzebne jest zrozumienie skutków potencjalnych błędów i niedopatrzeń. W artykule przedstawiono techniki, które mogą zostać wykorzystane w eksperymencie uczenia maszynowego. Opisano między innymi walidację prostą i krzyżową – z uwzględnieniem wyboru modelu – oraz podział czasowy. Przedstawiono wady i zalety wymienionych technik, uwzględniające między innymi rozmiar wejściowej bazy czy typ danych.
EN
The key aspect of machine learning is the model performance evaluation. Therefore, it is necessary to carefully plan the experiments. There is a need to understand the consequences of potential mistakes or omissions. This paper presents various techniques that can be used in a machine learning experiment. Simple split and cross validation – with or without model selection – as well as time split have been described. The advantages and disadvantages of these techniques have been presented – for example in terms of input database size or data type.
PL
W pracy przedstawiono analizę wydajności systemu komunikacyjnego i radaru MIMO traktowanych łącznie. Pozwala to na określenie granic efektywności tago systemu, w który jedno urządzenie jest uzależnione od drugiego. Dzięki temu jest możliwe jest zarządzanie wydajnością takiego systemu. Badania symulacyjne potwierdziły, że wydajność systemu komunikacyjnego współpracującego z radarem posiada swoje ograniczenia efektywności, które mogą ulegać zmianie.
EN
The paper presents analysis of the performance of communication system and MIMO radar treated as one system. This allows you to specify the limits of the capacity tago a system in which one device is dependent on another. Thanks to that it is possible to manage the performance of such a system. Simulation tests confirmed that the performance of the communication system that works with the radar has its limitations efficiency that may change.
EN
The supply chain of spare parts is the intersection between the supply chain, the after-sales and the maintenance services. Some authors have tried to define improvement paths in terms of models to satisfy the performance criteria. In addition, other authors are directed towards the integration of risk management in the demand forecasting and the stock management (performance evaluation) through probabilistic models. Among these models, the probabilistic graphical models are the most used, for example, Bayesian networks and petri nets. Performance evaluation is done through performance indicators. To measure the appreciation of the supply of the spare parts stock, this paper focuses on the performance evaluation of the system by petri nets. This evaluation will be done through an analytical study. The purpose of this study is to evaluate and analyze the performance of the system by proposed indicators. First, we present a literature review on Petri nets which is the essential tool in our modeling. Secondly, we present in the third section the analytical study of the model based on bath deterministic and stochastic petri networks. Finally, we present an analysis of the proposed model compared to the existing ones.
EN
Studies linking the use of lean practices to company performance have been increasing as markets are becoming more competitive and companies are eager for reducing waste and therefore implementing the Lean Management (LM) philosophy to improve performance. However, results from these studies have found various and different impacts and some light is needed. Extant literature was reviewed and, to achieve the research objective, a metaanalysis of correlations was carried out. The obtained results suggest a positive relationship between some lean practices and performance measures. Furthermore, the presence of moderators influencing the relationship between lean practices and performance outcomes is highlighted in our results. To our best knowledge, this is the first research that proposes a comparison of results from primary studies on Lean implementation, by analysing the linear relationship between lean practices and enterprise performance. It fills this gap and therefore represents an important contribution.
EN
This article presents the results of a survey using a questionnaire conducted in Algeria, to evaluate the quality of public drinking water service, and at the same time the level of dissatisfaction / satisfaction of the subscribers. A statistical analysis of the data has been conducted on a representative sample of general population to identify weaknesses and strengths related to the current state of water management. The assessment of the quality of service, and the quality of water, as well as the price of water under the influence of the geographical distribution of the population was also studied. The results of the statistical analyses show a wide variability regarding the level of dissatisfaction/satisfaction of the subscribers. In order to simplify the interpretation, we gathered the results in the form of classes and groups in such way that the cities appear on GIS mapping software, with their inhabitants’ degree of satisfaction.
PL
W artykule przedstawiono wyniki ankiety przeprowadzonej w Algierii metodą kwestionariuszy celem oceny jakości usług publicznego zaopatrzenia w wodę, a tym samym satysfakcji/niezadowolenia ankietowanych. Statystyczną analizę danych przeprowadzono na reprezentatywnej próbie generalnej populacji, aby określić mocne i słabe strony bieżącego stanu gospodarki wodnej. Przeprowadzono także ocenę jakości usług, jakości wody i ceny wody w odniesieniu do geograficznego rozmieszczenia ludności. Wyniki analiz statystycznych wskazują na duże zróżnicowanie poziomu satysfakcji/niezadowolenia ankietowanych. Aby uprościć interpretację, zebrano wyniki w postaci grup i klas w taki sposób, że miasta pojawiają się w graficznym programie GIS wraz z poziomem satysfakcji ich mieszkańców.
EN
Distances based on morphological operations have shown good performance in a number of applications. Still, the existing erosion and dilation distance for gray scale images can not be computed in all situations. Furthermore, it is possible that dissimilarity between objects which are compared grows strongly, but the value of a mentioned distance does not change. We present a proposition with the necessary and sufficient conditions for computing these morphological distances and discuss drawbacks that they possess. In addition, we propose novel morphological distances, which can be computed in all situations and provide results with desirable properties. The applicability of novel morphological distances is presented in illustrative examples, including their applicability to real data.
EN
This paper presents a performance evaluation of two simplified versions of the well-known basic weighted least squares algorithm for power system state estimation. Different simulations are tested on IEEE 14, 30 and 118 bus systems: a comparative study was carried out in order to identify the advantages and disadvantages of each method. The results bring out the interest of WLS2 Algorithm which reduces by half the computation time compared to the basic algorithm with the same reliability and precision.
PL
W artykule zaprezentowano badanie właściwości dwóch uproszczonych wersji algorytmu najmnijeszych kwadratów stosowanego do oceny systemu energetycznego. Przeprowadzono symulacje systemu IEEE z 134, 30 I 118 szynami. W algorytmie WLS2 udaje się zredukować o połowę czas obliczeń.
EN
This contribution discusses the usefulness of (max, +) algebra as a mathematical framework for a class of manufacturing systems. This class can be described as dynamic and asynchronous, where the state transitions are initiated by events that occur at di screte instants of time. An event corresponds to the start or the end of an activity. Such systems are known as discrete event systems (DES). An overview of the concepts of modelling and analysis using the (max, +) algebra approach to DES has been given. Also, examples of manufacturing systems have been provided to illustrate the potential of this approach. The type of production process used, such as serial line, assembly line, etc., influences the modelling of different basic manufacturing systems. We have also presented the impact of the capacity of interoperable buffers. Based on an analytical model, effectiveness and performance indexes have been evaluated.
13
Content available A fuzzy model for team control and its application
EN
An original fuzzy team control model is presented in this article. The model is based on a non-traditional combination of classical and contemporary achievements of management and mathematical theories of fuzzy logic and fuzzy sets. In methodological terms, the article also offers a set of tools for measuring and evaluating both team performance and the effectiveness of the team control system in the organization. Fuzzy tools and techniques for decision-making, studying of hidden effects and joint influences, and quantification of evaluations are employed in this set of tools. The suggested fuzzy model contributes to overcoming theoretical deficits on the issues of team control, and the methodology of team control fills a gap in the toolkit of team management. The results from verification of the fuzzy team control model at a small-sized Bulgarian enterprise are also discussed in this article. They indicate that it is possible to develop a fuzzy model for team control, increasing the effectiveness of the team control system in the enterprise.
14
Content available Performance Modeling of Database Systems: a Survey
EN
This paper presents a systematic survey of the existing database system performance evaluation models based on the queueing theory. The continuous evolution of the methodologies developed is classified according to the mathematical modeling language used. This survey covers formal models – from queueing systems and queueing networks to queueing Petri nets. Some fundamentals of the queueing system theory are presented and queueing system models are classified according to service time distribution. The paper introduces queueing networks and considers several classification criteria applicable to such models. This survey distinguishes methodologies, which evaluate database performance at the integrated system level. Finally, queueing Petri nets are introduced, which combine modeling power of queueing networks and Petri nets. Two performance models within this formalism are investigated. We find that an insufficient amount of research effort is directed into the area of NoSQL data stores. Vast majority of models developed focus on traditional relational models. These models should be adapted to evaluate performance of non-relational data stores.
EN
Because flexible manufacturing systems (FMS) are discrete event systems (DES), their modelling and control by means of Petri nets (PN) is widely used. While PN transitions are observable and controllable and PN places are measurable, place/transition PN (P/T PN) are suffcient for this aim. However, when some PN transitions are unobservable and/or uncontrollable and some places are non-measurable/unobservable, P/T PN are insufficient for modelling and especially for control. In such a case interpreted Petri nets (IPN) seem to be an appropriate replacement for P/T PN. In this paper a possibility of usage of IPN for FMS modelling and control is pointed out. Illustrative examples as well as the case study on a robotized assembly cell are introduced. By means of using timed PN (TPN) also the performance evaluation of the IPN model of controlled plant is accomplished whereby the simulation in Matlab.
EN
The Traffic Flow Description (TFD) option of the IP protocol is an experimental option, designed by the Authors and described by the IETF’s Internet Draft. This option was intended for signalling for QoS purposes. Knowledge about forthcoming traffic (such as the amount of data that will be transferred in a given period of time) is conveyed in the fields of the option between end-systems. TFD-capable routers on a path (or a multicast tree) between the sender and receiver(s) are able to read this information, process it and use it for bandwidth allocation. If the time horizons are short enough, bandwidth allocation will be performed dynamically. In the paper a performance evaluation of an HD video transmission QoS assured with the use of the TFD option is presented. The analysis was made for a variable number of video streams and a variable number of TCP flows that compete with the videos for the bandwidth of the shared link. Results show that the dynamic bandwidth allocation using the TFD option better assures the QoS of HD video than the classic solution, based on the RSVP protocol.
EN
Two-parameter phenomenological model for quantification of the cavitation damage process in its initial — incubation stage inspired by Förster energy migration theory is presented in the paper. The model built was supplemented with functional relationships between calculation parameters and strength parameters of the materials derived for chosen cavitation loading conditions. Experiments at the rotating disk set-up have been carried out in order to obtain necessary experimental data. The values of calculation parameters have been determined by adjusting the theoretical erosion curve to experimental one. Preliminary experimental verification of the model soundness consisted in comparing theoretical to experimental results obtained from both the ICET program and the experimental investigations of the cavitation erosion at Banki-Michel turbine blades. Reliability as well as the sources of inaccuracy and uncertainties were also discussed. The far-reaching aim of the work is to create the calculation tool for prediction of cavitation erosion performance in hydro-turbines during their operating cycle.
EN
In this work we perform extensive simulation studies to evaluate the mean packet waiting time in a system composed of two queues and Earliest Deadline First scheduler with different deadline distributions. The investigation is focused on the analysis of mean packet delays when deterministic and exponentially distributed deadline values are used. Comparing the results is targeted at deciding if the analytical approach proposed in our earlier work for modelling performance of Earliest Deadline First scheduler with exponentially distributed deadline values is also suitable when deadline values are deterministic. The series of simulation tests let us conclude the conditions when both deadline distributions produce very close results thus confirming the applicability of our already published analytical approach.
EN
In response to increased competition, manufacturing systems are becoming more complex in order to provide the flexibility and responsiveness required by the market. The increased complexity requires decision support tools that can provide insight into the effect of system changes on performance in an efficient and timely manner. This contribution discusses the usefulness of (max, +) algebra as a mathematical framework for a class of production systems. The class can be described as a dynamic and asynchronous where the state transitions are initiated by events that occur at discrete instants of time. An event corresponds to the start or the end of an activity. A common property of such examples is that the start of an activity depends on termination of several other activities. Such systems are known as discrete event systems (DES). In the paper an overview of the modeling and analysis concepts of the (max, +) algebra approach for DES is given. Also, an application examples from manufacturing systems are provided to illustrate the potential of this approach. Considered systems have been represented as (max, +) algebraic state space models. How to model different basic manufacturing systems depends on production type, like serial line, assembly line, etc. as well as impact of capacity of interoperable buffers have been presented. Based on an analytical model, effectiveness evaluation or performance indexes have been calculated for different configurations of the same production system. So, finally the best solution, for given criteria, has been obtained. All exemplary calculations have been made using the Max-Plus Algebra Toolbox for Matlab, the software package developed by author and available on his homepage.
EN
Cloud technologies are a very considerable area that influence IT infrastructure, network services and applications. Research has highlighted difficulties in the functioning of cloud infrastructure. For instance, if a server is subjected to malicious attacks or a force majeure causes a failure in the cloud’s service, it is required to determine the time that it takes the system to return to being fully functional after the crash. This will determine the technological and financial risks faced by the owner and end users of cloud services. Therefore, to solve the problem of determining the expected time before service is resumed after a failure, we propose to apply Markovian queuing systems, specifically a model of a multi-channel queuing system with Poisson input flow and denial-of-service (breakdown).
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