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Forcing Function (forcing + function)
Selected AbstractsA dynamic approach for evaluating parameters in a numerical methodINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 1 2005A. A. Oberai Abstract A new methodology for evaluating unknown parameters in a numerical method for solving a partial differential equation is developed. The main result is the identification of a functional form for the parameters which is derived by requiring the numerical method to yield ,optimal' solutions over a set of finite-dimensional function spaces. The functional depends upon the numerical solution, the forcing function, the set of function spaces, and the definition of the optimal solution. It does not require exact or approximate analytical solutions of the continuous problem, and is derived from an extension of the variational Germano identity. This methodology is applied to the one-dimensional, linear advection,diffusion problem to yield a non-linear dynamic diffusivity method. It is found that this method yields results that are commensurate to the SUPG method. The same methodology is then used to evaluate the Smagorinsky eddy viscosity for the large eddy simulation of the decay of homogeneous isotropic turbulence in three dimensions. In this case the resulting method is found to be more accurate than the constant-coefficient and the traditional dynamic versions of the Smagorinsky model. Copyright © 2004 John Wiley & Sons, Ltd. [source] Robust ,, filtering for uncertain differential linear repetitive processesINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 3 2008Ligang Wu Abstract The unique characteristic of a repetitive process is a series of sweeps or passes through a set of dynamics defined over a finite duration known as the pass length. At the end of each pass, the process is reset and the next time through the output, or pass profile, produced on the previous pass acts as a forcing function on, and hence contributes to, the dynamics of the new pass profile. They are hence a class of systems where a variable must be expressed in terms of two directions of information propagation (from pass-to-pass and along a pass, respectively) where the dynamics over the finite pass length are described by a matrix linear differential equation and from pass to pass by a discrete updating structure. This means that filtering/estimation theory/algorithms for, in particular, 2D discrete linear systems is not applicable. In this paper, we solve a general robust filtering problem with a view towards use in many applications where such an action will be required. Copyright © 2007 John Wiley & Sons, Ltd. [source] Relationship of habitat stability and intra-specific population dynamics of an obligate corallivore butterflyfishAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue S1 2005Michael P. Crosby Abstract 1.Intra-specific behavioural manifestations, as measured by territory size and conspecific agonistic encounters, population size and recruitment of the obligate corallivore butterflyfish Chaetodon multicinctus (Family: Chaetodontidae) were examined over a 5-year period at three Hawaiian coral reef sites, each receiving different levels of non-point-source terrigenous sediment runoff. 2.All three sites indicated significant correlations for percentage coral cover with territory size, fish size, and number of adult C. multicinctus, and for agonistic encounters with number of juvenile C. multicinctus. However, the site most impacted by sediment runoff indicated no significant correlations for percentage coral cover with territory size, fish length, number of adult C. multicinctus, number of agonistic encounters, or C. multicinctus juveniles; nor for number of agonistic encounters with number of juveniles. 3.The site moderately to minimally impacted by sediment runoff exhibited significant correlations for percentage coral cover with number of adults, while the site with no sedimentation impacts exhibited significant correlations for percentage coral cover with fish size, number of adults and number of juveniles. 4.Significant differences were found to exist between all three sites for agonistic encounters, territory size, fish size, number of C. multicinctus juveniles and percentage coral cover. The most highly impacted site exhibited a significantly higher number of adult C. multicinctus that were significantly smaller in size than either the minimally impacted and non-impacted sites. 5.The study design purposely selected high coral cover habitats (means ranged from 81.4% to 96.5%) at each site. Within this limited range of relatively high coral cover habitat, relative habitat stability resulting from a range of historic sediment inputs between sites appears to be the stronger forcing function for observed intra-specific behavioural manifestations, population size and recruitment than percentage coral cover. 6.Study results indicate that obligate corallivore butterflyfish behavioural manifestations, population size and recruitment may be used as a benchmark for changes in habitat stability for coral reef communities, and support the general premise of the butterflyfish indicator species hypothesis. Copyright © 2005 John Wiley & Sons, Ltd. [source] Equatorial magnetic helicity flux in simulations with different gaugesASTRONOMISCHE NACHRICHTEN, Issue 1 2010D. Mitra Abstract We use direct numerical simulations of forced MHD turbulence with a forcing function that produces two different signs of kinetic helicity in the upper and lower parts of the domain. We show that the mean flux of magnetic helicity from the small-scale field between the two parts of the domain can be described by a Fickian diffusion law with a diffusion coefficient that is approximately independent of the magnetic Reynolds number and about one third of the estimated turbulent magnetic diffusivity. The data suggest that the turbulent diffusive magnetic helicity flux can only be expected to alleviate catastrophic quenching at Reynolds numbers of more than several thousands. We further calculate the magnetic helicity density and its flux in the domain for three different gauges. We consider the Weyl gauge, in which the electrostatic potential vanishes, the pseudo-Lorenz gauge, where the speed of light is replaced by the sound speed, and the ,resistive gauge' in which the Laplacian of the magnetic vector potential acts as a resistive term. We find that, in the statistically steady state, the time-averaged magnetic helicity density and the magnetic helicity flux are the same in all three gauges (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Forced vibration testing of buildings using the linear shaker seismic simulation (LSSS) testing methodEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 7 2005Eunjong Yu Abstract This paper describes the development and numerical verification of a test method to realistically simulate the seismic structural response of full-scale buildings. The result is a new field testing procedure referred to as the linear shaker seismic simulation (LSSS) testing method. This test method uses a linear shaker system in which a mass mounted on the structure is commanded a specified acceleration time history, which in turn induces inertial forces in the structure. The inertia force of the moving mass is transferred as dynamic force excitation to the structure. The key issues associated with the LSSS method are (1) determining for a given ground motion displacement, xg, a linear shaker motion which induces a structural response that matches as closely as possible the response of the building if it had been excited at its base by xg (i.e. the motion transformation problem) and (2) correcting the linear shaker motion from Step (1) to compensate for control,structure interaction effects associated with the fact that linear shaker systems cannot impart perfectly to the structure the specified forcing functions (i.e. the CSI problem). The motion transformation problem is solved using filters that modify xg both in the frequency domain using building transfer functions and in the time domain using a least squares approximation. The CSI problem, which is most important near the modal frequencies of the structural system, is solved for the example of a linear shaker system that is part of the NEES@UCLA equipment site. Copyright © 2005 John Wiley & Sons, Ltd. [source] Dynamic ecosystem models and the evaluation of ecosystem effects of fishing: can we make meaningful predictions?AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 1 2003L.A. Robinson Abstract 1.Fishing is one of the most widespread anthropogenic impacts on marine ecosystems. In recent times, the development of measurable metrics of the resultant ecosystem effects, has become an important aspect of fisheries management. Ecosystem models are often advocated as tools for the evaluation of system effects, but the extent to which models are able to make meaningful predictions, has not yet been fully addressed. 2.In order to assess the suitability of models, to evaluate ecosystem effects of fisheries, the direct and indirect effects were catalogued. 3.From the literature, 33 applications of marine ecosystem models were identified for analysis of their ability to fully assess these catalogued effects. Analysis was possible for only 24 of the models due to poor documentation of the other 9. 4.Each model was examined for their inclusion of nine functional groups, deemed essential for the assessment of impacts of fishing on the whole ecosystem (e.g. detritus, marine mammals). The models were also assessed for their inclusion of several additional factors, either fundamental in the regulation of marine ecosystems (e.g. environmental forcing), or important in the classification of their role as a predictor of changes in ecological processes (e.g. simulation, spatial properties). 5.No model formulation provided coverage in all the areas necessary to cover the identified effects of fisheries. Eight models provided good coverage, nutrient dynamics and benthos were the least well represented aspects of the ecosystem. 6.The ECOPATH with Ecosim family of models, the European Regional Seas Ecosystem Model (ERSEM) and the Anderson & Ursin multispecies extension to the Beverton & Holt model all seem likely to yield good insights. 7.In further developing these models, however, consideration must be given to explicitly incorporate spatial factors and extrinsic forcing functions, such as climate. Copyright © 2002 John Wiley & Sons, Ltd. [source] Forcing Function Diagnostics for Nonlinear DynamicsBIOMETRICS, Issue 3 2009Giles Hooker Summary This article investigates the problem of model diagnostics for systems described by nonlinear ordinary differential equations (ODEs). I propose modeling lack of fit as a time-varying correction to the right-hand side of a proposed differential equation. This correction can be described as being a set of additive forcing functions, estimated from data. Representing lack of fit in this manner allows us to graphically investigate model inadequacies and to suggest model improvements. I derive lack-of-fit tests based on estimated forcing functions. Model building in partially observed systems of ODEs is particularly difficult and I consider the problem of identification of forcing functions in these systems. The methods are illustrated with examples from computational neuroscience. [source] How to create a large response from chaotic systems: Optimal forcing functions complement the natural dynamics of a systemCOMPLEXITY, Issue 4 2006Alfred W. Hübler No abstract is available for this article. [source] |