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Sökning: LAR1:umu > Chalmers tekniska högskola

  • Resultat 1-10 av 287
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1.
  • Abdulle, Assyr, et al. (författare)
  • High weak order methods for stochastic differential equations based on modified equations
  • 2012
  • Ingår i: SIAM Journal on Scientific Computing. - : Society for Industrial & Applied Mathematics (SIAM). - 1064-8275 .- 1095-7197. ; 34:3, s. A1800-A1823
  • Tidskriftsartikel (refereegranskat)abstract
    • Inspired by recent advances in the theory of modified differential equations, we propose a new methodology for constructing numerical integrators with high weak order for the time integration of stochastic differential equations. This approach is illustrated with the constructions of new methods of weak order two, in particular, semi-implicit integrators well suited for stiff (mean-square stable) stochastic problems, and implicit integrators that exactly conserve all quadratic firstintegrals of a stochastic dynamical system. Numerical examples confirm the theoretical results and show the versatility of our methodology.
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2.
  • Akkerman, V., et al. (författare)
  • Analysis of flame acceleration induced by wall friction in open tubes
  • 2010
  • Ingår i: Physics of Fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 22:5, s. 1-14
  • Tidskriftsartikel (refereegranskat)abstract
    • Spontaneous flame acceleration leading to explosion triggering in open tubes/channels due to wall friction was analytically and computationally studied. It was first demonstrated that the acceleration is affected when the thermal expansion across the flame exceeds a critical value depending on the combustion configuration. For the axisymmetric flame propagation in cylindrical tubes with both ends open, a theory of the initial (exponential) stage of flame acceleration in the quasi-isobaric limit was developed and substantiated by extensive numerical simulation of the hydrodynamics and combustion with an Arrhenius reaction. The dynamics of the flame shape, velocity, and acceleration rate, as well as the velocity profile ahead and behind the flame, have been determined. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3425646]
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3.
  • Akkerman, V., et al. (författare)
  • Flow-flame interaction in a closed chamber
  • 2008
  • Ingår i: Physics of Fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 20:5, s. 21-
  • Tidskriftsartikel (refereegranskat)abstract
    • Numerous studies of flame interaction with a single vortex and recent simulations of burning in vortex arrays in open tubes demonstrated the same tendency for the turbulent burning rate proportional to U-rms lambda(2/3), where U-rms is the root-mean-square velocity and lambda is the vortex size. Here, it is demonstrated that this tendency is not universal for turbulent burning. Flame interaction with vortex arrays is investigated for the geometry of a closed burning chamber by using direct numerical simulations of the complete set of gas-dynamic combustion equations. Various initial conditions in the chamber are considered, including gas at rest and several systems of vortices of different intensities and sizes. It is found that the burning rate in a closed chamber (inverse burning time) depends strongly on the vortex intensity; at sufficiently high intensities it increases with U-rms approximately linearly in agreement with the above tendency. On the contrary, dependence of the burning rate on the vortex size is nonmonotonic and qualitatively different from the law lambda(2/3). It is shown that there is an optimal vortex size in a closed chamber, which provides the fastest total burning rate. In the present work, the optimal size is six times smaller than the chamber height.
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6.
  • Anton, Rikard, et al. (författare)
  • A fully discrete approximation of the one-dimensional stochastic heat equation
  • 2020
  • Ingår i: IMA Journal of Numerical Analysis. - : Oxford University Press. - 0272-4979 .- 1464-3642. ; 40:1, s. 247-284
  • Tidskriftsartikel (refereegranskat)abstract
    • A fully discrete approximation of the one-dimensional stochastic heat equation driven by multiplicative space–time white noise is presented. The standard finite difference approximation is used in space and a stochastic exponential method is used for the temporal approximation. Observe that the proposed exponential scheme does not suffer from any kind of CFL-type step size restriction. When the drift term and the diffusion coefficient are assumed to be globally Lipschitz this explicit time integrator allows for error bounds in Lq(Ω), for all q ≥ 2, improving some existing results in the literature. On top of this we also prove almost sure convergence of the numerical scheme. In the case of nonglobally Lipschitz coefficients, under a strong assumption about pathwise uniqueness of the exact solution, convergence in probability of the numerical solution to the exact solution is proved. Numerical experiments are presented to illustrate the theoretical results.
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7.
  • Anton, Rikard, et al. (författare)
  • Exponential integrators for stochastic Schrödinger equations driven by Itô noise
  • 2018
  • Ingår i: Journal of Computational Mathematics. - : Global Science Press. - 0254-9409 .- 1991-7139. ; 36:2, s. 276-309
  • Tidskriftsartikel (refereegranskat)abstract
    • We study an explicit exponential scheme for the time discretisation of stochastic Schr¨odinger Equations Driven by additive or Multiplicative Itô Noise. The numerical scheme is shown to converge with strong order 1 if the noise is additive and with strong order 1/2 for multiplicative noise. In addition, if the noise is additive, we show that the exact solutions of the linear stochastic Schr¨odinger equations satisfy trace formulas for the expected mass, energy, and momentum (i. e., linear drifts in these quantities). Furthermore, we inspect the behaviour of the numerical solutions with respect to these trace formulas. Several numerical simulations are presented and confirm our theoretical results.
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8.
  • Antona-Makoshi, Jacobo, et al. (författare)
  • Accident analysis to support the development of strategies for the prevention of brain injuries in car crashes
  • 2018
  • Ingår i: Accident Analysis and Prevention. - : Elsevier BV. - 0001-4575 .- 1879-2057. ; 117, s. 98-105
  • Tidskriftsartikel (refereegranskat)abstract
    • This study estimated the frequency and risk of Moderate-to-Maximal traumatic brain injuries sustained by occupants in motor vehicle crashes in the US. National Automotive Sampling System - Crashworthiness Data System crashes that occurred in years 2001–2015 with light vehicles produced 2001 or later were incorporated in the study. Crash type, crash severity, car model year, belt usage and occupant age and sex were controlled for in the analysis. The results showed that Moderate concussions account for 79% of all MAIS brain 2+ injuries. Belted occupants were at lower risks than unbelted occupants for most brain injury categories, including concussions. After controlling for the effects of age and crash severity, belted female occupants involved in frontal crashes were estimated to be 1.5 times more likely to sustain a concussion than male occupants in similar conditions. Belted elderly occupants were found to be at 10.5 and 8 times higher risks for sub-dural haemorrhages than non-elderly belted occupants in frontal and side crashes, respectively. Adopted occupant protection strategies appear to be insufficient to achieve significant decreases in risk of both life-threatening brain injuries and concussions for all car occupants. Further effort to develop occupant and injury specific strategies for the prevention of brain injuries are needed. This study suggests that these strategies may consider prioritization of life-threatening brain vasculature injuries, particularly in elderly occupants, and concussion injuries, particularly in female occupants.
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9.
  • Antona-Makoshi, Jacobo, et al. (författare)
  • Analysis of Traumatic Brain Injuries Sustained by Occupants in Japanese Brand Car Crashes in the US
  • 2018
  • Ingår i: International Journal of Automotive Engineering. - : Society of Automotive Engineers of Japan. - 2185-0992 .- 2185-0984. ; 9:3, s. 145-450
  • Tidskriftsartikel (refereegranskat)abstract
    • This study estimates, by means of an analysis of accident data from the US, the incidence and risk of car crash related traumatic brain injuries for occupants in Japanese brand cars. The study incorporated crash type, crash severity, car model year, belt use and the victim's age and sex. Concussion risk was the highest among all brain injury categories for all crash types and severities; females were at higher risks than males. When concussions were excluded, Subdural Haemorrhages, Intracranial Haemorrhages and Sub-Arachnoid Haemorrhages comprised the most frequent injury categories. Elderly occupants were at considerably higher risks than non-elderly for these bleeding injuries.
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10.
  • Arbid, Yara, et al. (författare)
  • Use of iron-bearing waste materials in laundry wastewater treatment
  • 2024
  • Ingår i: Journal of Water Process Engineering. - : Elsevier. - 2214-7144. ; 57
  • Tidskriftsartikel (refereegranskat)abstract
    • This study evaluates the efficiency of a steel waste-derived magnetite (WM) for the treatment of laundry wastewater under various irradiation conditions (ultraviolet-A and C: UVA and UVC), both in the presence and absence of H2O2. Because WM can contain magnetite and elemental iron phases, its ability to remove ciprofloxacin and phenol, here used as model pollutants, and total organic carbon (TOC) from laundry wastewater was compared with that of synthetic magnetite (SM) and zero-valent iron (ZVI). We show that the mixed ZVI/H2O2 system under UVC degraded up to 80 % of the pollutant and 70 % of the TOC. WM had, on the other hand, a lower reactivity for pollutants due to the presence of inorganic impurities, yet removed up to 60 % of TOC. In all cases considered in this work, a higher degradation rate was observed under UVC irradiation than under UVA. Moreover, iron-based materials can adsorb heavy metals co-existing in the laundry wastewater. Recyclability tests showed no significant loss in the activity of WM or SM for up to 5 cycles in laundry wastewater. This study can have strong implications for the development of new remediation technologies relying on industrial solid wastes, especially in the context of a circular economy.
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