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- Malmberg, Anders, et al.
(författare)
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A real-time assimilation algorithm applied to near-surface ocean wind fields
- 2008
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Ingår i: Environmetrics. - : Wiley. - 1099-095X .- 1180-4009. ; 19:3, s. 319-330
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedMarine operations depend on the ability to forecast suddenly appearing storms, and failures often cause great damage. As part of a sea-state alarm study, meteorological forecasts overlaid with satellite observations sent to ships have been found to be a useful too]. In this paper we present a real-time assimilation algorithm that extends this tool using statistical methods. The algorithm is applied to near-surface ocean wind fields. A Kalman filter based on a spatio-temporal state-space model provides a basis for emulation of the atmospheric model. The main contribution of this paper is the algorithm that makes it possible to use the information in the satellite observations over the full spatial domain of interest at a real-time basis.
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| 2. |
- Malmberg, Anders, et al.
(författare)
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Forecasting near-surface ocean winds with Kalman filter techniques
- 2005
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Ingår i: Ocean Engineering. - : Elsevier BV. - 1873-5258 .- 0029-8018. ; 32:3-4, s. 273-291
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Tidskriftsartikel (refereegranskat)abstract
- In this paper a statistical forecasting model designed for bounded areas of near-surface ocean wind speeds is implemented. Dimension reduction is achieved by decomposing the covariance structure into one large-scale and one small-scale component using empirical orthogonal functions. The large-scale component is modelled with an AR process and forecasts are calculated by applying a Kalman filter. The model is suited for stable weather situations as for unsteady situations it requires more frequent wind information. From the prediction variance fields it is possible to identify where unexpected weather usually enters the area.
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| 3. |
- Åberg, Sofia, et al.
(författare)
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An image warping approach to spatio-temporal modelling
- 2005
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Ingår i: Environmetrics. - : Wiley. - 1099-095X .- 1180-4009. ; 16:8, s. 833-848
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Tidskriftsartikel (refereegranskat)abstract
- In this article we present a spatio-temporal dynamic model that can be realized using image warping. Image warping is a non-linear deformation which maps every point in one image plane to a point in another image plane. Using thin-plate splines, these deformations are defined by how a small set of points is mapped, making the method computationally tractable. In our case the dynamics of the process is modelled by thin-plate spline deformations and how they vary in time. Thus we make no assumption of stationarity in time. Finding the deformation between two images in the space-time series is a trade-off between a good match of the images and, a smooth, physically plausible, deformation. This is formulated as a penalized likelihood problem, where the likelihood measures how good the match is and the penalty comes from a prior model on the deformation. The dynamic model we suggest can be used to make forecasts and also to estimate the uncertainties associated with these. An introduction to image warping and thin-plate splines is given as well as an application where the methodology is applied to the problem of nowcasting radar precipitation.
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| 4. |
- Andersson, Fredrik, et al.
(författare)
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A Fast, Bandlimited Solver for Scattering Problems in Inhomogeneous Media
- 2005
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Ingår i: Journal of Fourier Analysis and Applications. - : Springer Science and Business Media LLC. - 1531-5851 .- 1069-5869. ; 11:4, s. 471-487
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Tidskriftsartikel (refereegranskat)abstract
- The numerical treatment of two-dimensional scattering in inhomogeneous media is considered. A novel approach in treating convolution operators with low regularity is used to construct an iterative solver for the Lippmann-Schwinger integral equation. In this way, accurate approximations within a choice of bandwidth can be obtained in a rapid manner. The performance of the method is tested on a discontinuous scattering object for which the exact solution is known.
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| 7. |
- Asplund, Maria, 1978-, et al.
(författare)
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Incidence of traumatic peripheral nerve injuries and amputations in Sweden between 1998 and 2006
- 2008
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Ingår i: Neuroepidemiology. - Basel : Kargel, AG. - 0251-5350 .- 1423-0208.
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Tidskriftsartikel (refereegranskat)abstract
- Background: To define the epidemiological pattern of nerve injuries and traumatic amputations in Sweden, 1998-2006, and investigate possible targets for emerging neural engineering and neuroprosthetic technologies. Methods: The Swedish Hospital Discharge Register was used as basis of information, including data from all public in-patient care, excluding out-patient data. ICD-10 codes were screened for nerve injuries and traumatic amputations of high incidence or in-patient care time. Selected codes, causing factors, age and gender distribution were discussed in detail, and potential targets for tailored solutions were identified. Results: Incidence rate was determined to 13.9 for nerve injuries and 5.21 for amputations per 100 000 person-yrs. The majority of injuries occurred at wrist and hand level although it could be concluded that these are often minor injuries requiring less than a week of hospitalization. The single most care consuming nerve injury was brachial plexus injury constituting, in average, 68 injuries and 960 hospital days annually. When minor amputations of fingers and toes were disregarded, most frequent site of amputation was between knee and ankle (24 patients / year). Conclusions: Based on analysis of incidence and care time, we find that brachial plexus injuries and lower leg amputations should be primary targets of these new technologies.
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| 8. |
- Bohlin, Markus, et al.
(författare)
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Optimization of condition-based maintenance for industrial gas turbines: Requirements and results
- 2009
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Ingår i: Proceedings of the ASME Turbo Expo Volume 5. - 9780791848869 ; , s. 455-464
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Konferensbidrag (refereegranskat)abstract
- In oil and gas applications, the careful planning and execution of preventive maintenance is important due to the high costs associated with shutdown of critical equipment. Optimization and lifetime management for equipment such as gas turbines is therefore crucial in order to achieve high availability and reliability. In this paper, a novel condition-based gas turbine maintenance strategy is described and evaluated. Using custom-madegas turbine maintenance planning software, maintenance is repeatedly reoptimized to fit into the time intervals where production losses are least costly and result in the lowest possible impact. The strategy focuses on accurate online lifetime estimates for gas turbine components, where algorithms predicting future maintenance requirements are used to produce maintenance deadlines. This ensures that the gas turbines are maintained in accordance with the conditions on site. To show the feasibility and economic effects of a customer-adapted maintenance planning process, the maintenance plan for a gas turbine used in a real-world scenario is optimized using a combinatorial optimization algorithm and input from gas turbine operation data, maintenance schedules and operator requirements. The approach was validated through the inspection of a reference gas turbine after a predetermined time interval. It is shown that savings may be substantial compared to a traditional preventivemaintenance plan. In the evaluation, typical cost reductions range from 25 to 65 %. The calculated availability increase in practice is estimated to range from 0.5 to 1 %. In addition, down-time reductions of approximately 12 % are expected, due solely to improved planning. This indicates significant improvements.
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