| 1. |
- Karen Barbosa de Melo, A., et al.
(författare)
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INFLUENCE OF BACKTRACKING AT SOLAR-TRACKING PHOTOVOLTAIC POWER PLANTS FOR GENERATION AND PROTECTION
- 2019
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Ingår i: Energy Proceedings. - : Scanditale AB.
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Konferensbidrag (refereegranskat)abstract
- Photovoltaic plants appear as an option for a more environmentally friendly centralized generation. Solar-tracking is used for efficiency gain presenting better performance than fixed tilted plants. However, the system suffers generation and protection problems without the use of backtracking algorithms. Shading conditions can prejudice the energy generation and cause diode failure. This paper studies the influence of backtracking for protection and generation. For protection, it is shown that the bypass diode takes time to activate, generating hotspots. For efficiency, the production and plant size gains are highlighted.
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| 2. |
- Curtin, W. A., et al.
(författare)
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Hybrid discrete dislocation models for fatigue crack growth
- 2010
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Ingår i: International Journal of Fatigue. - : Elsevier BV. - 1879-3452 .- 0142-1123. ; 32:9, s. 1511-1520
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Tidskriftsartikel (refereegranskat)abstract
- A framework for accurately modeling fatigue crack growth in ductile crystalline solids is necessarily multiscale The creation of new free surface occurs at the atomistic scale, where the material's cohesive strength is controlled by the local chemistry On the other hand, significant dissipation during fatigue crack growth takes place at a size scale that can be modeled appropriately by conventional continuum mechanics. The intermediate size scale where the discreteness of dislocations comes Into play is the main origin of the hysteresis needed for fatigue and of the high stresses required for atomistic separation to take place. We focus on recent developments which permit analyses of fatigue crack growth involving the direct coupling of disparate size scales. Although no analyses have been carried out directly coupling size scales from the atomic to the conventional continuum, the ingredients to do so are in place. We provide background that illustrates the key role played by the intermediate discrete dislocation size scale and review steps that have been taken to permit direct size scale coupling. The prospects and modeling needs for further developments are also discussed (C) 2009 Elsevier Ltd All rights reserved.
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| 3. |
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| 4. |
- Curtin, W. A., et al.
(författare)
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Multi-scale plasticity modeling : Coupled discrete dislocation and continuum crystal plasticity
- 2008
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Ingår i: Advances in Heterogeneous Material Mechanics 2008 - 2nd International Conference on Heterogeneous Material Mechanics, ICHMM 2008. - 9781932078800 ; , s. 320-320
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Konferensbidrag (refereegranskat)abstract
- A hierarchical multiscale model that couples a region of material described by discrete dislocation plasticity1 to a surrounding region described by conventional crystal plasticity is presented. The coupled model captures size-dependent plasticity phenomena, such as dislocation structuring and formation of geometrically necessary dislocations, that can occur at the micron scale while also capturing the plastic flow, and associated energy dissipation, at much larger scales where size-dependent effects are minimal. The key to the model is the treatment of the interface between the discrete and continuum regions, where continuity of tractions and displacements is maintained in an average sense and the flow of burgers vector via "passing" of discrete dislocations is managed. The model is validated through uniaxial plane-strain tension tests which show that the coupled model deforms similarly to both single-scale models. The multiscale model is then applied to study crack growth, where both near-tip dislocation structures and far-field plastic dissipation are crucial to the overall toughening. Results show that the toughening is nearly independent of the size of the discrete dislocation plasticity region around the crack tip down to 5um, simultaneously validating the model and identifying the lengths scales over which size dependence plays a role in this problem. The multiscale model reduces the computational burden of discrete dislocation plasticity modeling substantially with little or no loss of fidelity in the predictions of material behavior, thereby greatly extending the range of discrete dislocation modeling. Future work will combine this method with the Coupled Atomistic/Discrete-Dislocation2 model developed by one of the co-authors, leading to a true atom-to-continuum multiscale model for metallic materials.
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| 5. |
- Grigoriev, I. A., et al.
(författare)
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Explicit algebraic and differential Reynolds stress model application to homogeneously sheared and compressed turbulence
- 2015
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Ingår i: Proceedings - 15th European Turbulence Conference, ETC 2015. - : TU Delft.
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Konferensbidrag (refereegranskat)abstract
- An explicit algebraic and differential Reynolds stress models (EARSM and DRSM) are used to investigate the influence of homogeneous shear and compression on the behaviour of turbulence in the limit of rapid distortion theory (RDT). EARSM is shown to give realizable results and to preserve RDT regime, unlike the eddy-viscosity model (EVM). The DRSM version of our model is in reasonable agreement with RDT theory.
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| 6. |
- Izosimov, Viacheslav, et al.
(författare)
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Requirement Decomposition and Testability in Development of Safety-Critical Automotive Components
- 2012
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Konferensbidrag (refereegranskat)abstract
- 2ISO26262 is a recently approved standard for functional safety in road vehicles. It provides guidelines on minimization of unreasonable safety risks during development of embedded systems in road vehicles. However, the development process specified in ISO26262 involves a number of steps that will require changing traditional and well established development processes. In a transition phase, however, due to lack of tool support, the steps may be performed manually, increasing the risk for delays and increased cost. This paper describes a case study in which we have successfully worked with traceability and testability of functional safety requirements, as well as safety requirements assigned to a testing tool that automates integration and verification steps, leading to standard-compliant tool qualification. Our tool qualification method employs fault injection as a validation method to increase confidence in the tool. Our case study will help to avoid many of the new pitfalls that can arise when attempting to realize standard-compliant development.
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| 7. |
- Wallin, M, et al.
(författare)
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Pressurized Circulating Fluid Bed Gasification Reactor
- 1994
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Ingår i: 29th Intersociety Energy Conversion Engineering Conference: August 7-11, 1994, Monterey, CA : a collection of technical papers. - 1563470918 ; , s. 1543-1548
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Konferensbidrag (refereegranskat)
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| 8. |
- Wallin, Stefan, et al.
(författare)
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Bridging between coarse and fine resolution in variable resolution turbulence computations
- 2012
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Ingår i: THMT-12. PROCEEDINGS OF THE SEVENTH INTERNATIONAL SYMPOSIUM ON TURBULENCE, HEAT AND MASS TRANSFER. - : BEGELL HOUSE, INC. ; , s. 1171-1177
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Konferensbidrag (refereegranskat)abstract
- Variable-resolution (VR) bridging turbulence calculations in the context of partially-averaged Navier-Stokes (PANS) approach have been conducted by adopting explicit terms for the energy transfer between the resolved and unresolved scales when the resolution is varying in time. The method is tested for decaying isotropic turbulence flow. It is demonstrated that the energy transfer terms dissipates the correct amount of resolved turbulence kinetic energy for decreasing resolution and is also able to produce the necessary resolved turbulence in the case of increasing resolution while conserving the total amount of turbulence energy. Time-developing mixing layer simulations are ongoing. Preliminary results show that the mixing growth rate is reasonably preserved for different rate of resolution, but that the response to variable resolution is somewhat too strong.
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| 9. |
- Adalbjornsson, S. I., et al.
(författare)
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Estimating Periodicities in Symbolic Sequences Using Sparse Modeling
- 2015
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Ingår i: Ieee Transactions on Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1053-587X .- 1941-0476. ; 63:8, s. 2142-2150
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we propose a method for estimating statistical periodicities in symbolic sequences. Different from other common approaches used for the estimation of periodicities of sequences of arbitrary, finite, symbol sets, that often map the symbolic sequence to a numerical representation, we here exploit a likelihood-based formulation in a sparse modeling framework to represent the periodic behavior of the sequence. The resulting criterion includes a restriction on the cardinality of the solution; two approximate solutions are suggested-one greedy and one using an iterative convex relaxation strategy to ease the cardinality restriction. The performance of the proposed methods are illustrated using both simulated and real DNA data, showing a notable performance gain as compared to other common estimators.
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| 10. |
- Balocco, C, et al.
(författare)
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Microwave detection at 110 GHz by nanowires with broken symmetry
- 2005
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 5:7, s. 1423-1427
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Tidskriftsartikel (refereegranskat)abstract
- By using arrays of nanowires with intentionally broken symmetry, we were able to detect microwaves up to 110 GHz at room temperature. This is, to the best of our knowledge, the highest speed that has been demonstrated in different types of novel electronic nanostructures to date. Our experiments showed a rather stable detection sensitivity over a broad frequency range from 100 MHz to 110 GHz. The novel working principle enabled the nanowires to detect microwaves efficiently without a dc bias. In principle, the need for only one high-resolution lithography step and the planar architecture allow an arbitrary number of nanowires to be made by folding a linear array as many times as required over a large area, for example, a whole wafer. Our experiment on 18 parallel nanowires showed a sensitivity of approximately 75 mV dc output/mW of nominal input power of the 110 GHz signal, even though only about 0.4% of the rf power was effectively applied to the structure because of an impedance mismatch. Because this array of nanowires operates simultaneously, low detection noise was achieved, allowing us to detect -25 dBm 110 GHz microwaves at zero bias with a standard setup.
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