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- Cantwell, C. D., et al.
(författare)
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Nektar plus plus : An open-source spectral/hp element framework
- 2015
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Ingår i: Computer Physics Communications. - : Elsevier BV. - 0010-4655. ; 192, s. 205-219
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Tidskriftsartikel (refereegranskat)abstract
- Nektar++ is an open-source software framework designed to support the development of high-performance scalable solvers for partial differential equations using the spectral/hp element method. High-order methods are gaining prominence in several engineering and biomedical applications due to their improved accuracy over low-order techniques at reduced computational cost for a given number of degrees of freedom. However, their proliferation is often limited by their complexity, which makes these methods challenging to implement and use. Nektar++ is an initiative to overcome this limitation by encapsulating the mathematical complexities of the underlying method within an efficient C++ framework, making the techniques more accessible to the broader scientific and industrial communities. The software supports a variety of discretisation techniques and implementation strategies, supporting methods research as well as application-focused computation, and the multi-layered structure of the framework allows the user to embrace as much or as little of the complexity as they need. The libraries capture the mathematical constructs of spectral/hp element methods, while the associated collection of pre-written PDE solvers provides out-of-the-box application-level functionality and a template for users who wish to develop solutions for addressing questions in their own scientific domains. Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland No. of lines in distributed program, including test data, etc.: 1052456 No. of bytes in distributed program, including test data, etc.: 42851367 External routines: Boost, PFTW, MPI, BLAS, LAPACK and METIS (www.cs.umn.edu) Nature of problem: The Nektar++ framework is designed to enable the discretisation and solution of time-independent or time-dependent partial differential equations. Running time: The tests provided take a few minutes to run. Runtime in general depends on mesh size and total integration time.
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- Bigoni, D., et al.
(författare)
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Efficient uncertainty quantification of a fully nonlinear and dispersive water wave model with random inputs
- 2016
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Ingår i: Journal of Engineering Mathematics. - : Springer Science and Business Media LLC. - 0022-0833 .- 1573-2703. ; 101:1, s. 87-113
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Tidskriftsartikel (refereegranskat)abstract
- A major challenge in next-generation industrial applications is to improve numerical analysis by quantifying uncertainties in predictions. In this work we present a formulation of a fully nonlinear and dispersive potential flow water wave model with random inputs for the probabilistic description of the evolution of waves. The model is analyzed using random sampling techniques and nonintrusive methods based on generalized polynomial chaos (PC). These methods allow us to accurately and efficiently estimate the probability distribution of the solution and require only the computation of the solution at different points in the parameter space, allowing for the reuse of existing simulation software. The choice of the applied methods is driven by the number of uncertain input parameters and by the fact that finding the solution of the considered model is computationally intensive. We revisit experimental benchmarks often used for validation of deterministic water wave models. Based on numerical experiments and assumed uncertainties in boundary data, our analysis reveals that some of the known discrepancies from deterministic simulation in comparison with experimental measurements could be partially explained by the variability in the model input. Finally, we present a synthetic experiment studying the variance-based sensitivity of the wave load on an offshore structure to a number of input uncertainties. In the numerical examples presented the PC methods exhibit fast convergence, suggesting that the problem is amenable to analysis using such methods.
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- Björklund, Erland, et al.
(författare)
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Supercritical Fluid Extraction
- 2005
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Ingår i: Encyclopedia of Analytical Science. - 0127641009 ; , s. 597-604
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
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- Campos, J, et al.
(författare)
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On the interaction between adsorbed layers of monoolein and the lipase action on the formed layers
- 2002
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Ingår i: Colloids and Surfaces B: Biointerfaces. - 1873-4367 .- 0927-7765. ; 26:1-2, s. 172-182
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Tidskriftsartikel (refereegranskat)abstract
- We used the Surface Force Apparatus (SFA) and ellipsometry techniques to study the interaction forces and the adsorption behavior of monoolein (MO), respectively. MO was adsorbed from water to a hydrophobised mica or silica surface. In addition the effect of added lipase, Thermomyces (Humicula) lanuginosa lipase (TLL), to an adsorbed layer of MO was investigated. The force versus distance curves between two MO covered surfaces feature a strong repulsive interaction beneath 400 A. The range of the repulsive force decreases, however, with the number of approaches. No adhesion was observed, provided that the surfaces were not taken to hydrophobic contact. The surface separation at MO-MO contact was determined to about 55 Angstrom This means a layer thickness of about 27 Angstrom, which is comparable to the thickness (25 Angstrom) determined by ellipsometry. The repulsive force may arise from compression of a cubic phase of MO. This phase are suggested to form between the surfaces when they approach close contact due to capillary induced phase separation (CIPS) from the saturated MO solution. The repulsive force changes significantly with time after addition of TLL (concentration of about 1 x 10(-8) M). In contrast to the force curves recorded before adding TLL, the surfaces do not seem to be completely covered with MO as we always observed an attractive force (inward jump) of similar range as was observed between pure OTE surfaces. Ellipsometry measurement of TLL action on MO covered hydrophobic surface reveals a significant and sharp decrease of the amounts adsorbed. Furthermore, the rate of decrease and reduction in adsorbed amount increased with TLL concentration. (C) 2002 Elsevier Science B.V. All rights. reserved.
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- Davidsson, K.O., et al.
(författare)
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Countermeasures against alkali-related problems during combustion of biomass in a circulating fluidized bed boiler
- 2008
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Ingår i: Chemical Engineering Science. - : Elsevier. - 0009-2509 .- 1873-4405. ; 63:21, s. 5314-5329
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this work was to study different ways to mitigate alkali-related problems during combustion of biomass in circulating fluidized beds. Wood chips and wood pellets were fired together with straw pellets, while the tendency to agglomerate and form deposits was monitored. In addition to a reference case, a number of countermeasures were applied in related tests. Those were addition of elemental sulphur, ammonium sulphate and kaolin to a bed of silica sand, as well as use of olivine sand and blast-furnace slag as alternative bed materials. The agglomeration temperature, composition and structure of bed-ash samples were examined. The flue-gas composition, including gaseous alkali chlorides, was measured in the hot flue gases and in the stack. Particles in the flue gas were collected and analysed for size distribution and composition. Deposits were collected on a probe in hot flue gases and their amount and composition were analysed. Addition of kaolin was found to be the best method to counteract the agglomeration problem. The deposition problem is effectively counteracted with addition of ammonium sulphate, while kaolin is too expensive to be used commercially against deposits, and sulphur is less effective than ammonium sulphate.
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- Eskilsson, Claes, 1971, et al.
(författare)
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On devising Boussinesq-type models with bounded eigenspectra: One horizontal dimension
- 2014
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Ingår i: Journal of Computational Physics. - : Elsevier BV. - 1090-2716 .- 0021-9991. ; 271, s. 261-280
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Tidskriftsartikel (refereegranskat)abstract
- The propagation of water waves in the nearshore region can be described by depthintegrated Boussinesq-type equations. The dispersive and nonlinear characteristics of the equations are governed by tuneable parameters. We examine the associated linear eigenproblem both analytically and numerically using a spectral element method of arbitrary spatial order p. It is shown that existing sets of parameters, found by optimising the linear dispersion relation, give rise to unbounded eigenspectra which govern stability. For explicit time-stepping schemes the global CFL time-step restriction typically requires Delta t proportional to p(-2). We derive and present conditions on the parameters under which implicitlyimplicit Boussinesq-type equations will exhibit bounded eigenspectra. Two new bounded versions having comparable nonlinear and dispersive properties as the equations of Nwogu (1993) and Schaffer and Madsen (1995) are introduced. Using spectral element simulations of stream function waves it is illustrated that (i) the bounded equations capture the physics of the wave motion as well as the standard unbounded equations, and (ii) the bounded equations are computationally more efficient when explicit time-stepping schemes are used. Thus the bounded equations were found to lead to more robust and efficient numerical schemes without compromising the accuracy.
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