Hydro reservoir handling in Norway before and after deregulation

The Norwegian Energy Act that came into force in 1991 deregulated the electricity market and removed the former obligation power companies had to supply electricity to the geographical area they were responsible for. Hence producers can supply electricity on the basis of profitability. In 2007 the Energy Act was evaluated by the Government. As a part of this, a study concerning hydro reservoir handling before and after deregulation was carried out by SINTEF. Public statistics show that average hydro reservoir levels measured in per cent of reservoir capacity have been reduced after 1990. We have used the power-market model EMPS¹ (EFI's Multi-area Power-market Simulator) to analyze if this reduction can be explained by natural variation in climatic variables or by structural changes that have occurred after 1990. Simulation results show that the reduced reservoir levels cannot be explained by natural variation in climatic variables. Structural changes such as increased transmission capacities can, however, explain some of the reduction. Our study does not indicate that the present reservoir handling gives reservoir levels that are too low. In this paper we also describe the stochastic dynamic optimization problem for long-term hydropower scheduling, and we explain how this problem actually is solved by the EMPS model.     

Reliability against fracture of butt welds as inferred from inspection data

Butt welds under static stress may suffer fracture due to a crack growing quickly from some defect in the weld. Nondestructive inspection for defects needs a rational criterion for acceptance of a weld. The paper demonstrates that recent results in structural reliability theory applied to defect fracture systems may constitute a basis for a criterion for highly reliable welds. It takes into account uncertainty from several sources. Essential uncertainty is due to the high degree of idealization of the widely used standard fracture mechanical criterion of crack initiation. Also the indirect measurement of the defect sizes contributes significantly. Finally the statistical uncertainty due to small sample sizes cannot be neglected. Besides the distribution of defect sizes the number of defects in the weld has importance. Only an estimate is needed of the mean number of defects. Statistical uncertainty of this estimate has very low importance for the total reliability of the weld.     

The fake of reliability measures as absolutes

It is claimed that any reliability measure defined in connection with a limit state theory of a high reliability technological system is a purely formal comparative measure of safety. It only makes sense to make comparisons within classes of “similar” technological systems which are all accessible to the same theory. Interpretation of calculated formal failure probabilities as predictions of real failure rates are generally not justified.     

Influence of a glass-water interface on the on-axis trapping of micrometer-sized spherical objects by optical tweezers

A systematic study of the influence of a glass-water interface on the on-axis trapping of micrometer-sized spherical objects by optical tweezers is presented. The ways in which the escape force and the trapping position, as well as the stiffness of the trap, depend on the focusing depth, the numerical aperture, and the degree of overfilling of the objective entrance pupil are investigated. It is concluded, among other things, that objectives with the highest numerical aperture and the use of large degrees of overfilling do not always provide the optimum trapping conditions at finite depths.     

Characterization of background signals in wavelength-modulation spectrometry in terms of a fourier based theoretical formalism

The detectability of wavelength-modulation (WM) diode-laser spectrometric techniques is frequently limited by various background signals. A new theoretical formalism for WM spectrometry, based on Fourier analysis and therefore capable of handling a variety of phenomena including the characterization and the analysis of analytical as well as background WM signals, was recently presented [Appl. Opt. 38, 5803 (1999)]. We report a detailed characterization of WM background signals from multiple reflections between pairs of surfaces in the optical system that act as etalons and from the associated intensity modulation in terms of this new formalism. The agreement between the background signals from a thin glass plate and those predicted by the formalism is good, which verifies the new Fourier analysis-based formalism.     

Oil Spill Detection in Radarsat and Envisat SAR Images

We present algorithms for automatic detection of oil spills in synthetic aperture radar (SAR) images. The algorithms consist of three main parts, namely: 1) detection of dark spots; 2) feature extraction from the dark spot candidates; and 3) classification of dark spots as oil spills or look-alikes. The algorithms have been trained on a large number of Radarsat and Envisat Advanced Synthetic Aperture Radar (ASAR) images. The performance of the algorithm is compared to manual and semiautomatic approaches in a benchmark study using 59 Radarsat and Envisat images. The algorithms can be considered to be a good alternative to manual inspection when large ocean areas are to be inspected     

Principles of engineering safety: Risk and uncertainty reduction

This article provides a systematised account of safety engineering practices that clarifies their relation to the goal of safety engineering, namely to increase safety. We list 24 principles referred to in the literature of safety engineering, dividing them into four major categories: Inherently safe design, Safety reserves, Safe fail and Procedural safeguards. It emerges from this systematisation that important aspects of these methods can be better understood with the help of the distinction between risk and uncertainty.     

The Energy Concept Adviser—A tool to improve energy efficiency in educational buildings

Educational buildings such as kindergartens, schools and universities display many similar design, operation and maintenance features in most countries. The two most noteworthy similarities amongst these building types are the high energy consumption and the necessity for retrofitting many buildings within this sector. However, studies have shown that during retrofit, energy saving measures are only rarely applied, because the decision-makers lack knowledge of investments and the efficiency of potential energy saving measures. The main goal of the International Energy Agency ECBCS Annex 36 is to provide the educational building decision-makers with sufficient data, information and tools to improve their learning and teaching environments by improving the energy efficiency of their buildings.     

Duration of visit to critical set by Gaussian process

The exact distribution of the duration of a visit of a stationary Gaussian process to an interval is not known except for processes with certain simple auto-dependence properties of Markov type. However, the exact mean is known without any restrictive dependence assumptions.Since the duration distribution, or, equivalently, the first outpassage time distribution, is needed in several engineering applications, there is an interest in making the necessary simplifying assumptions concerning the auto-dependence properties of the process. For smooth wide band processes comparisons with simulated results show that it improves the accuracy of the results considerably if a Markov type property, called 0-lag dependence of the first passage time, is imposed on the Slepian model process rather than if it is imposed directly on the original stationary process. The Slepian model process describes the distributional behaviour of the original stationary and ergodic Gaussian process after a crossing into the interval.The resulting duration distribution formulas involve multiple integrals and are therefore numerically complicated. For practical applications a simple three-parameter distribution family is suggested such that it possesses the exact mean. The three parameters may be estimated by fit to some few points obtained by numerical calculation of the multiple integrals.