| 1. |
- Röding, Magnus, et al.
(författare)
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Machine learning-accelerated small-angle X-ray scattering analysis of disordered two- and three-phase materials
- 2022
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Ingår i: Frontiers in Materials. - : Frontiers Media S.A.. - 2296-8016. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Small-angle X-ray scattering (SAXS) is a useful technique for nanoscale structural characterization of materials. In SAXS, structural and spatial information is indirectly obtained from the scattering intensity in the spectral domain, known as the reciprocal space. Therefore, characterizing the structure requires solving the inverse problem of finding a plausible structure model that corresponds to the measured scattering intensity. Both the choice of structure model and the computational workload of parameter estimation are bottlenecks in this process. In this work, we develop a framework for analysis of SAXS data from disordered materials. The materials are modeled using Gaussian Random Fields (GRFs). We study the case of two phases, pore and solid, and three phases, where a third phase is added at the interface between the two other phases. Further, we develop very fast GPU-accelerated, Fourier transform-based numerical methods for both structure generation and SAXS simulation. We demonstrate that length scales and volume fractions can be predicted with good accuracy using our machine learning-based framework. The parameter prediction executes virtually instantaneously and hence the computational burden of conventional model fitting can be avoided. Copyright © 2022 Röding, Tomaszewski, Yu, Borg and Rönnols.
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| 2. |
- Tahvili, Sahar, et al.
(författare)
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Solving complex maintenance planning optimization problems using stochastic simulation and multi-criteria fuzzy decision making
- 2014
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Ingår i: 10TH INTERNATIONAL CONFERENCE ON MATHEMATICAL PROBLEMS IN ENGINEERING, AEROSPACE AND SCIENCES: ICNPAA 2014 Conference date: 15–18 July 2014 Location: Narvik, Norway ISBN: 978-0-7354-1276-7 Editor: Seenith Sivasundaram Volume number: 1637 Published: 10 december 2014. - : American Institute of Physics (AIP). - 9780735412767 ; , s. 766-775
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Konferensbidrag (refereegranskat)abstract
- One of the most important factors in the operations of many cooperations today is to maximize profit and one important tool to that effect is the optimization of maintenance activities. Maintenance activities is at the largest level divided into two major areas, corrective maintenance (CM) and preventive maintenance (PM). When optimizing maintenance activities, by a maintenance plan or policy, we seek to find the best activities to perform at each point in time, be it PM or CM. We explore the use of stochastic simulation, genetic algorithms and other tools for solving complex maintenance planning optimization problems in terms of a suggested framework model based on discrete event simulation.
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| 3. |
- Tahvili, Sahar, et al.
(författare)
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Strategic maintenance planning by fuzzy AHP and Markov Decision Processes
- 2015
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Ingår i: ASMDA 2015 Proceedings. - : ISAST: International Society for the Advancement of Science and Technology. - 9786185180058 ; , s. 991-1004, s. 297-310
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Konferensbidrag (refereegranskat)abstract
- The work of engineering and business professionals includes making a series of decisions and optimizations. Real world decision making problems faced by decision makers (DM) involve multiple, usually conflicting, criteria. These multicriteria decision making problems (MCDM) are usually complicated and large in scale. In strategic Maintenance planning, choices are made on where to focus time and effort, where to spend money. We consider a framework for strategic maintenance planning in a modern maintenance driven organization. Our focus is on a multi-stage framework in which the planning is divided into two stages, identifying an optimal set of possible actions and finding the optimal decision policy for these actions for each point in time as a function of the stochastically evolving system state. To this respect we consider the MCDM method of AHP (Analytical hierarchical programming) in a fuzzy environment, and Markov decision processes (MDP).
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| 4. |
- Wandebäck, Fredrik, et al.
(författare)
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Variation Feedback and 3D Visualization of Geometrical Inspection Data
- 2010
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Ingår i: Proceedings of the ASME 2009 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference IDETC/CIE, August 30 - September 2, 2009, San Diego, California, USA. - 9780791849057 ; 8, s. 197-208
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Konferensbidrag (refereegranskat)abstract
- There is no type of manufacturing process that is not afflicted by variation. Activities intended to ensure the quality of a company's geometry processes are usually referred to as geometry assurance activities. One clear industrial problem is to understand the relations between the products concept and the manufacturing process. Dimensional data is a very important source of experience of how a product's geometry has worked in the interaction with the actual manufacturing system. Users therefore need good analysis and presentation tools of geometry outcomes to support both the product developers and production engineers in the analysis of the production output and its consequences. Today the dimensional data can be difficult to obtain or access, and is not necessarily presented in such a way as to provide the user with all necessary information. This paper presents how presentation and analysis tools of geometrical inspection data can be taken a step further. New functionality for feature based 3D visualization of inspection data has been developed which integrates the variation simulation platform and the inspection data database. The goal has been to create better tools for analysis of geometrical variation and increase the understanding of the sources of variation.
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| 5. |
- Alexandersson, Martin, et al.
(författare)
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A comparison of ship manoeuvrability models to approximate ship navigation trajectories
- 2023
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Ingår i: Ships and Offshore Structures. - : Taylor and Francis Ltd.. - 1744-5302 .- 1754-212X. ; 18:4, s. 550-557
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Tidskriftsartikel (refereegranskat)abstract
- It is essential to describe a ship’s manoeuvrability for various applications, e.g. optimal control of unmanned surface vehicles (USVs). In this study, the capability of two recognised manoeuvrability models to predict ships’ trajectories is investigated based on both simulation and open-water experiment test data. The parameters of these models are estimated by a statistical learning method. The goodness of the two estimated models for describing a merchant ship’s manoeuvrability is first studied using her manoeuvring simulation data. Then, experimental manoeuvring tests to use a USV in open water with wind and drifting effects are used to check the conventional model identification procedures. Finally, some modifications and adjustments are proposed to improve the conventional procedures. It shows that the proposed procedures can accurately derive the ship’s manoeuvrability based on experimental data. © 2022 The Author(s).
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| 6. |
- Eslamian, Morteza, et al.
(författare)
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An Accurate Method for Leakage Inductance Calculation of Shell-Type Multi Core-Segment Transformers With Circular Windings
- 2021
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Ingår i: IEEE Access. - 2169-3536. ; 9, s. 111417-111431
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Tidskriftsartikel (refereegranskat)abstract
- The leakage field in shell-type transformers is strongly affected by the boundary conditions introduced by the core walls and thus the effect of the core should be considered properly in the leakage inductance calculation. In this paper, a new method for accurate calculation of the leakage inductance of shell-type multi core-segment transformers with circular windings is presented. For this purpose, first, the expressions for self and mutual inductances are derived in cylindrical coordinates considering the core walls as the flux-normal boundary condition. Then, a new approach is proposed for calculating the leakage inductance considering the number and dimensions of the used core segments. The method is developed at first for single and double core-segment transformers (known also as E-core and U-core transformers) and then adopted for shell-type segmented-core transformers. The method is verified by 3-D FEM simulations. The comparisons with the previous analytical methods demonstrate the superiority of the proposed method. A transformer prototype has been built and verification tests have been conducted. The comparisons show that the leakage inductance can be estimated with an error less than 1%, demonstrating a very high accuracy with the proposed method.
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| 7. |
- Di Rocco, Sandra, et al.
(författare)
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Computing Geometric Feature Sizes for Algebraic Manifolds
- 2023
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Ingår i: SIAM JOURNAL ON APPLIED ALGEBRA AND GEOMETRY. - : Society for Industrial & Applied Mathematics (SIAM). - 2470-6566. ; 7:4, s. 716-741
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Tidskriftsartikel (refereegranskat)abstract
- We introduce numerical algebraic geometry methods for computing lower bounds on the reach, local feature size, and weak feature size of the real part of an equidimensional and smooth algebraic variety using the variety's defining polynomials as input. For the weak feature size, we also show that nonquadratic complete intersections generically have finitely many geometric bottlenecks, and we describe how to compute the weak feature size directly rather than a lower bound in this case. In all other cases, we describe additional computations that can be used to determine feature size values rather than lower bounds.
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| 8. |
- Johannesson, Pär, 1969, et al.
(författare)
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Mechanical reliability analysis of flexible power cables for marine energy
- 2022
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Ingår i: Journal of Marine Science and Engineering. - : MDPI AG. - 2077-1312. ; 10:6, s. 1-
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Tidskriftsartikel (refereegranskat)abstract
- Marine power cables connected to moving devices at sea may experience millions of load cycles per year, and thus they need to be flexible due to the movements of the cable and designed for mechanical loads. In this study, the focus is on the mechanical life of flexible low- and medium voltage power cables connecting devices to hubs. The reliability design method Variational Mode and Effect Analysis (VMEA) is applied, based on identifying and quantifying different types of uncertainty sources, including scatter, model and statistical uncertainties. It implements a load–strength approach that combines numerical simulations to assess the loads on the cable and experimental tests to assess the strength of the cable. The VMEA method is demonstrated for an evaluation of bending fatigue, and is found to be a useful tool to evaluate uncertainties in fatigue life for WEC (Wave Energy Converter) system cables during the design phase. The results give a firm foundation for the evaluation of safety against fatigue and are also helpful for identifying weak spots in the reliability assessment, thereby motivating actions in the improvement process. Uncertainties in terms of scatter, statistical uncertainty and model uncertainty are evaluated with respect to theWaveEL 3.0, a WEC designed by the companyWaves4Power, and deployed in Runde, Norway. A major contribution to the overall uncertainty is found to originate from the fatigue life model, both in terms of scatter and model uncertainty.
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| 9. |
- Kuznecovs, Artjoms, 1990, et al.
(författare)
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Ultimate limit state analysis of a double-hull tanker subjected to biaxial bending in intact and collision-damaged conditions
- 2020
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Ingår i: Ocean Engineering. - : Elsevier Ltd. - 0029-8018 .- 1873-5258. ; 209
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Tidskriftsartikel (refereegranskat)abstract
- This study presents a comparison between nonlinear finite element analysis (FEA) and the Smith method of Fujikubo et al. (2012). The objective was to compare the accuracy and computation effort of the two methods for a double-hull tanker under biaxial bending and various ship conditions: intact hull structure, collision-damaged hull structure, newly built condition, and ship hull aged due to corrosion. The results for the non-corroded and intact ship hull structures showed good agreement between FEA, the Smith method and IACS CSR-H for vertical bending loading conditions. For all other bending load combinations, FEA always gave lower ultimate bending moments than the Smith method. The differences between the two methods were larger for the corroded and damaged ship hull structure than for other conditions. Results from ultimate strength analyses of the collision-damaged hull structures showed that both methods captured the expected asymmetric ultimate strength response due to asymmetric damage. A residual strength index calculation showed that the reduction was larger for the FEA than for the Smith method. A procedure is proposed that combines results of a few FEAs with the advantages of the Smith method to generate accurate biaxial bending load interaction curves for different ship conditions. © 2020 Elsevier Ltd
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| 10. |
- Röding, Magnus, 1984, et al.
(författare)
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Computational Screening of Diffusive Transport in Nanoplatelet-Filled Composites: Use of Graphene to Enhance Polymer Barrier Properties
- 2018
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Ingår i: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 1:1, s. 160-167
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Tidskriftsartikel (refereegranskat)abstract
- Motivated by the substantial interest in various fillers to enhance the barrier properties of polymeric films, especially graphene derivatives, we perform a computational screening of obstructed diffusion to explore the design parameter space of nanoplatelet-filled composites synthesized in silico. As a model for the nanoplatelets, we use circular and elliptical nonoverlapping and impermeable flat disks, and diffusion is stochastically simulated using a random-walk model, from which the effective diffusivity is calculated. On the basis of 4000 generated structures and diffusion simulations, we systematically investigate the impact of different nanoplatelet characteristics such as orientation, layering, size, polydispersity, shape, and amount. We conclude that the orientation, size, and amount of nanoplatelets are the most important parameters and show that using nanoplatelets oriented perpendicular to the diffusion direction, under reasonable assumptions, with approximately 0.2% (w/w) graphene, we can reach 90% reduction and, with approximately 1% (w/w) graphene, we can reach 99% reduction in diffusivity, purely because of geometrical effects, in a defect-free matrix with perfect compatibility. Additionally, our results suggest that the existing analytical models have some difficulty with extremely large aspect ratio (extremely flat) nanoplatelets, which calls for further development.
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