Urho Pulkkinen

Application of stochastic filtering for lifetime prediction

This paper introduces a stochastic filtering modeling approach for predicting the remaining lifetime of a component based on information on the stochastic degradation process and uncertain condition monitoring measurements. The model is illustrated by a case study, where the degradation is assumed to be a simplified fatigue crack growth process. The model accounts for uncertainties in both degradation process and condition measurements in a sound way. If completed with information on costs of monitoring, failure and replacement, such model could be used in optimizing both the condition monitoring intervals and, e.g. the replacement time for the component.

MEASURING THE SAFETY EFFECT OF RAISED BICYCLE CROSSINGS USING A NEW RESEARCH METHODOLOGY

Before-and-after study methodology was developed and applied to evaluating the effect on bicyclists’ safety of raising urban bicycle crossings by 4 to 12 cm. In total, 44 junctions were reconstructed in this way in Gothenburg, Sweden. Four of these were studied in detail. Before the implementations, bicyclists were riding either in the roadway or on separate paths parallel to the roadway. The paths then ended with short ramps or curb cuts at each cross street, and bicyclists used nonelevated, marked bicycle crossings, similar to pedestrian crosswalks but delineated by white painted rectangles rather than zebra stripes. The results show that the paths with raised crossings attracted more than 50 percent more bicyclists and that the safety per bicyclist was improved by approximately 20 percent due to the increase in bicycle flow, and with an additional 10 to 50 percent due to the improved layout. However, the increased bicyclist volume means that the total number of bicycle accidents is expected to increase. Besides accident analysis, the change in risk was estimated using four different methods: surveys of bicyclists and experts, respectively; conflict data; and a quantitative expert model. Using a Bayesian approach for combining the results shows that the most likely effect of raising the bicycle crossing is a risk reduction of around 30 percent, compared with the before situation with a conventional bicycle crossing. Motorists and pedestrians also saw safety benefits from this traffic-calming measure.

Models for non-destructive inspection data

Abstract This paper describes the use of statistical models for the evaluation of the reliability of non-destructive inspections. Probability models for the uncertainty in the flaw size determination and the flaw detection are constructed. The flaw sizing models are based on the assumption that the measured and true flaw sizes are related in a simple way: two models based on logarithmic and logit transformations of the flaw sizes are considered. The probability of flaw detection is assumed to depend on the flaw size either through logarithmic or logit transformation. To illustrate the use of these models, they have been applied to flaw sizing data and flaw detection frequency data. Furthermore, models for Bayesian updating of flaw size distributions were developed. In this connection, models for updating the size distribution of a single flaw as well as for handling multiple flaws are introduced.

AN EXPERT JUDGMENT MODEL APPLIED TO ESTIMATING THE SAFETY EFFECT OF A BICYCLE FACILITY

This paper presents a risk index model that can be used for assessing the safety effect of countermeasures. The model estimates risk in a multiplicative way, which makes it possible to analyze the impact of different factors separately. Expert judgments are incorporated through a Bayesian error model. The variance of the risk estimate is determined by Monte-Carlo simulation. The model was applied to assess the safety effect of a new design of a bicycle crossing. The intent was to gain safety by raising the crossings to reduce vehicle speeds and by making the crossings more visible by painting them in a bright color. Before the implementations, bicyclists were riding on bicycle crossings of conventional Swedish type, i.e. similar to crosswalks but delineated by white squares rather than solid lines or zebra markings. Automobile speeds were reduced as anticipated. However, it seems as if the positive effect of this was more or less canceled out by increased bicycle speeds. The safety per bicyclist was still improved by approximately 20%. This improvement was primarily caused by an increase in bicycle flow, since the data show that more bicyclists at a given location seem to benefit their safety. The increase in bicycle flow was probably caused by the new layout of the crossings since bicyclists perceived them as safer and causing less delay. Some future development work is suggested. Pros and cons with the used methodology are discussed. The most crucial parameter to be added is probably a model describing the interaction between motorists and bicyclists, for example, how risk is influenced by the lateral position of the bicyclist in relation to the motorist. It is concluded that the interaction seems to be optimal when both groups share the roadway.

A method for analysing the reliability of a transmission grid

The paper describes a probabilistic method for transmission grid security evaluation. Power system security is the ability of the power system to withstand sudden disturbances such as short circuits. The method presented here uses event and fault trees and combines them with power system dynamic simulations. Event trees model the substation protection and trip operations after line faults. Different event tree end states (fault duration, circuit breaker trips) are simulated with power system dynamic analysis program. The dynamic analysis results (power system post-fault states) are then classified into secure, alert, emergency and system breakdown. The probabilities, minimal cut sets and grid level importance measures (Fussell-Vesely, risk increase and decrease factors) are calculated for the total and partial system breakdown. In this way, the relative importance of the substation devices regarding to the system breakdown can be reached. Also the more and less likely contributing factors to system breakdown are received. With this method, an existing 400 kV transmission grid with its line fault and device failure statistics is analysed.

A Multi-Criteria Mathematical Programming Model for Agile Virtual Organization Creation

This paper studies virtual organization (VO) creation through an application of mathematical programming. We present a mixed integer linear programming (MILP) model to support VO configuration in a virtual organization breeding environment (VBE). The model allows for multiple criteria, of which we give several examples: One objective is to minimize total fixed and variable costs. Another objective is to maximize expected cooperative efficiency using collaboration history as reference data. We model collaboration history with bilateral cooperation indices forming a weighted graph of VBE members. Furthermore, we incorporate capacity risk-measures in the model, allowing capacity risk minimization.

Methods for combination of expert judgements

Abstract The problem of combining expert probability distributions is discussed. The approach adopted here is based on information-theoretic considerations. Combination procedures based on minimization of the sums of the Kullback-information between the expert distributions and the aggregated distribution are derived. The aggregated distributions are shown to be proportional to the geometric or arithmetic average of the expert distributions. The approach is then applied to some simple cases where the expert distributions belong to some families of probability distributions.

An integrated approach to human reliability analysis — decision analytic dynamic reliability model

Abstract The reliability of human operators in process control is sensitive to the context. In many contemporary human reliability analysis (HRA) methods, this is not sufficiently taken into account. The aim of this article is that integration between probabilistic and psychological approaches in human reliability should be attempted. This is achieved first, by adopting such methods that adequately reflect the essential features of the process control activity, and secondly, by carrying out an interactive HRA process. Description of the activity context, probabilistic modeling, and psychological analysis form an iterative interdisciplinary sequence of analysis in which the results of one sub-task maybe input to another. The analysis of the context is carried out first with the help of a common set of conceptual tools. The resulting descriptions of the context promote the probabilistic modeling, through which new results regarding the probabilistic dynamics can be achieved. These can be incorporated in the context descriptions used as reference in the psychological analysis of actual performance. The results also provide new knowledge of the constraints of activity, by providing information of the premises of the operator’s actions. Finally, the stochastic marked point process model gives a tool, by which psychological methodology may be interpreted and utilized for reliability analysis.

Comparison of approaches for estimating pipe rupture frequencies for risk-informed in-service inspections

Abstract This paper describes the comparative study of two approaches to estimate pipe leak and rupture frequencies for piping. One method is based on a probabilistic fracture mechanistic model while the other one is based on statistical estimation of rupture frequencies from a large database. In order to be able to compare the approaches and their results, the rupture frequencies of some selected welds have been estimated using both of these methods. This paper highlights the differences both in methods, input data, need and use of plant specific information and need of expert judgement. The study focuses on one specific degradation mechanism, namely the intergranular stress corrosion cracking. This is the major degradation mechanism in old stainless steel piping in BWR environment, and its growth is influenced by material properties, stresses and water chemistry.

Encouraging suppliers to process innovations: a game theory approach

This paper studies the design of process-innovation incentives in supplier networks. A real-life case study from the boat-building industry is presented to illustrate the importance of explicitly encouraging suppliers to continuous improvement. Motivated by the case study, we constructed a game theory model trying to capture the possible conflicting interests of different parties in a company network. Using our model, we applied three different bargaining rules in order to determine ex-ante profit-sharing principles that award process-innovations. The aim of profit sharing is that the efficiency-improving arrangements can be implemented so that none of the network companies has to incur losses. Consequently, if the profit-sharing principles are ex-ante contracted, then the network companies have the incentive to innovate.