JPSRA 2012 Volume 3, Number 2
Zamojski Wojciech Dependability of a discrete transport system
A discrete system performing transport tasks (carriage of goods between the starting and ending points) using the vehicles of limited capacity and reliability is analyzed. The quality of transport tasks depend on the availability of transportation means (cars, roads, etc.), their functional properties (services) and reliability (faults and renewals) and of the system organization (dispatchers / system managers). Unfriendly system events affecting the realization of transport tasks are classified. A dependability model of the discrete transport system is considered as an unreliable service network. Outlined the idea of a maintenance policy system and a problem of synthesis of the discrete transport system. [full text]
Mazurkiewicz Jacek, Nowak Katarzyna, Walkowiak Tomasz Fuzzy approach to complex system analysis
The paper presents a new approach to reliability and functional analysis of sophisticated complex systems using fuzzy logic. We propose to use such methodology since dependability parameters of the system are mostly approximated by experts instead of classical sources of data. Presented approach show different idea – modeling system using the unified structure – in functional sense. We assess the reliability of the system by accumulated down time. Fuzzy logic based reliability analysis, as well as Computer Information System and Discrete Transport System modeling and simulation are presented. Moreover, results of numerical experiment performed on a test case scenario related to the economic and functional aspects using proposed methodology are given. Fuzzy approach allows reducing the problem of assumptions of reliability distributions and – this way – seems to be very interesting for real systems management and tuning. [full text]
Sugier Jarosław Implementation of symmetric block ciphers in popular-grade FPGA devices
In this paper we discuss hardware implementations of the two best ciphers in the AES contest – the winner Rijndael and the Serpent – in low-cost, popular Field-Programmable Gate Arrays (FPGA). After presenting the elementary operations of the ciphers and organization of their processing flows we concentrate on specific issues of their implementations in two selected families of popular-grade FPGA devices from Xilinx: currently the most common Spartan-6 and its direct predecessor Spartan-3. The discussion concentrates on differences in resources offered by these two families and on efficient implementation of the elementary transformations of the two ciphers. For case studies we propose a selection of different architectures (combinational, pipelined and iterative) for the encoding units and, after their implementation, we compare size requirements and performance parameters of the two ciphers across different architectures and on different FPGA platforms. [full text]
Walkowiak Tomasz Web server performance and availability model for simulation
The paper presents an approach to modelling and simulation of web systems. The systems are being modelled from the point of view of services realized by them. The formal model of a system, accompanied with a model of a request realization is presented. The main aspect of the paper is a simulation model of client-server interactions that adequately describes the relationship between the server response time, its availability and resource utilization. The model was constructed based on the the results of multiple experiments presented in a paper. Moreover, it was implemented in the simulation tool and its accuracy verified against testbed web servers. Apache and IIS servers were analysed. [full text]
Skrzypczak Izabela The fuzzy method in the compound conformity criteria of concrete strength as quality and safety control
Non-random uncertainty character connected with the evaluation and classification of concrete compressive strength, and also faults and disadvantages of statistical compliance criteria, were reasons to formulate a new fuzzy criterion of concrete strength assessment and classification procedure of produced concrete. Membership functions of mean value of compressive strength, included in conformity criteria, have been determined in the contribution on the basis of fuzzy-statistical experiment. [full text]
Tchórzewska-Cieślak Barbara, Rak Janusz Ryszard, Piegdoń Izabela Risk analysis of water supply interruptions in collective water supply systems
The subject and main purpose of this study is to present the method of risk analysis and assessment of the lack of water supply to the collective water supply system (CWSS). Presented method using the expected value of water scarcity. The analysis was based on all possible states of the operation of water production subsystem. The article contains calculation example of analysis for the exemplary CWSS with regard to absolute risk, equal to the expected value of water scarcity and the relative risk referred to the nominal value of the water demand. In the example attached special importance to the criteria levels of the relative risk of lack of water supply. Presented method is a new concept which allows to make comprehensive analysis of reliability, safety and operation of the collective water supply system. [full text]
Grabski Franciszek Random Failure Rate
The reliability function defined by a failure rate which is a stochastic process with nonnegative and right continuous trajectories is presented in this paper. The reliability function with an at most countable state space semi-Markov failure rate process is investigated. A theorem concerning of equations for a conditional reliability function with a semi-Markov process as a failure rate is presented in this paper. The solutions of the proper renewal equations allow getting the reliability functions for the finite space semi-Markov random walk, for the Poisson process and for the Furry-Yule process as a failure rate. [full text]
Barnert Tomasz, Kosmowski Kazimierz T., Śliwiński Marcin Framework for RIDM within functional safety management process
The functional safety management in life cycle is a complex process starting with identifying hazards and defining safety-related functions (SRFs) with regard to the results of risk assessment oriented at determining the safety integrity level of consecutive functions. Another element of such process is a verification of required SIL for considered architectures of safety-related system that implements given safety function. Due to complexity of the problem, to overcome difficulties in safety-related decision making often under considerable uncertainties, usually without taking into account security aspects, we propose to apply the RIDM methodology oriented on functional safety management of programmable control and protection systems in life cycle taking into some more important risk-related factors identified. [full text]
Smolarek Leszek Bayesian approach to shipping reliability and safety
In a Bayesian approach, there are two main sources of information about parameters of interest such as prior beliefs or the prior distribution of the parameter and the likelihood of observing the data given our expectations about the parameter. The prior distribution may be based on previous studies, literature reviews or expert opinions and indicates how we believe the parameter would behave if we had no data upon which to base our judgments. In case where we have less data, the prior has greater influence. The maximum likelihood estimate predominates only when we have a lot of data. The posterior distribution is the result of combining the prior distribution and the likelihood. In the paper the examples of using Bayes approach to shipping operational reliability and safety is presented. [full text]
Blokus Roszkowska Agnieszka, Montewka Jakub, Smolarek Leszek Modelling the accident probability in large-scale, maritime transportation system
The probability of an accident in transportation systems can serve as a measure of these systems safety or risk, depending on the objective. Therefore numerous methods and models for risk evaluation, with respect to maritime, have been developed. However, these models are either too simplified, allowing relatively fast analysis but very often missing the substantial links among the model variables, or they are too slow for effective analysis, due to computational complexity, not necessarily being backed-up with the complexity of the model itself. Thereby, this paper introduces a novel method evaluating the probability of ship-ship collision in the maritime transportation system focusing on the open sea collisions, applying the queuing theory in the simulation model. The model allows relatively fast prediction as it focuses on the specific events (e.g. accidents), instead of simulating the whole traffic. To support this hypothesis a case study is presented focusing on a selected element of transportation system in operation. [full text]
Mazurek Jolanta, Smolarek Leszek Estimation of surrounding the spillage time
This article presents the model of oil spill on the grid graph. We consider the three types of grid which parameters are corresponding to condition on the sea. The firefighter problem gives the algorithm to bound the oil spill. We compare the action starting time in model described by sum of N variables with the uniform probability distribution and the action starting time in real situation described by sum of two triangular random variables. For every type of grid we determine the Time Average of Going Around of the Spill. [full text]
Wachnicka Joanna Modelling selected road safety measures at the regional level in Europe
Regions are Europe’s basic levels of management. The literature was reviewed to identify regional safety analyses and some of the factors that are important for road safety in the regions. Next, data were collected at the regional NUTS 2 level in Europe for the years 1999-2008. An analysis of the data helped identify factors which have the strongest bearing on fatalities and other safety measures. This paper presents the initial results of a broader research programme on road safety at the regional level. [full text]
Bajorek Grzegorz, Kiernia-Hnat Marta, Skrzypczak Izabela Operating characteristic curves in monitoring of strength in ready-mixed concrete
Statistical conformity criteria for compressive strength of concrete are the matter debate. Statistical criteria can have prejudicial effects to quality and safety of construction. The paper is concerned with the application of operating-characteristic curves to the monitoring of compressive strength in ready-mixed concrete. In this paper the crude Monte Carlo simulation method has been applied to obtain OC-curves for different compound conformity criteria and normal distribution type of concrete strength. [full text]
Kołowrocki Krzysztof, Soszyńska-Budny Joanna Reliability prediction and optimization of complex technical systems with application in port transport
There are presented the methods of the reliability prediction and optimization of complex technical systems related to their operation processes. The general model of the reliability of complex technical systems operating at variable operation conditions linking the semi-Markov modeling of their operation processes with the multistate approach to their reliability analysis and the linear programming are applied in maritime industry to the reliability and risk prediction and optimization of the container gantry crane. [full text]