Lashckarbolok M.,Iran University of Science and Technology |
Jabbari E.,Iran University of Science and Technology |
Vuik K.,Delft Institute of Applied Mathematics
Scientia Iranica | Year: 2014
A simple node enrichment strategy using a gradient based error estimator is presented for the Collocated Discrete Least Squares (CDLS) meshless method. Also, a procedure is defined to distribute collocation points according to the field nodes position. Here, shape functions are constructed using the Radial Point Interpolation Method (RPIM). As temporal discretization, a first-order accurate scheme, named the semi-incremental fractional step method, is used. One of the advantages of this scheme is its capability of using large time step sizes for the solution of governing equations on steady state problems. The capability of the presented strategy is shown by investigating the Carreau-Yasuda uid flow model in solving lid-driven cavity flow problems with different curve fitting indices values. © 2014 Sharif University of Technology. All rights reserved.
Baayen J.H.,Weserstrasse 153 |
Baayen J.H.,Delft Institute of Applied Mathematics |
Ockels W.J.,ASSET Institute
IET Control Theory and Applications | Year: 2012
A novel tracking paradigm for flying geometric trajectories using tethered kites is presented. It is shown how the differential-geometric notion of turning angle can be used as a one-dimensional representation of the kite trajectory, and how this leads to a single-input single-output tracking problem. Based on this principle a Lyapunov-based non-linear adaptive controller is developed that only needs control derivatives of the kite aerodynamic model. The resulting controller is validated using simulations with a point-mass kite model. © The Institution of Engineering and Technology 2011.
van den Berg P.L.,Delft Institute of Applied Mathematics |
Kommer G.J.,VU University Amsterdam |
Zuzakova B.,VU University Amsterdam |
Zuzakova B.,Charles University
Operations Research for Health Care | Year: 2016
Since ambulance providers are responsible for life-saving medical care at the scene in emergency situations and since response times are important in these situations, it is crucial that ambulances are located in such a way that good coverage is provided throughout the region. Most models that are developed to determine good base locations assume strict 0-1 coverage given a fixed base location and demand point. However, multiple applications require fractional coverage. Examples include stochastic, instead of fixed, response times and survival probabilities. Straightforward adaption of the well-studied MEXCLP to allow for coverage probabilities results in a non-linear formulation in integer variables, limiting the size of instances that can be solved by the model. In this paper, we present a linear integer programming formulation for the problem. We show that the computation time of the linear formulation is significantly shorter than that for the non-linear formulation. As a consequence, we are able to solve larger instances. Finally, we will apply the model, in the setting of stochastic response times, to the region of Amsterdam, the Netherlands. © 2015 Elsevier Ltd.
Purkiani K.,Leibniz Institute for Baltic Sea Research |
Becherer J.,Leibniz Institute for Baltic Sea Research |
Floser G.,Helmholtz Center Geesthacht |
Grawe U.,Leibniz Institute for Baltic Sea Research |
And 3 more authors.
Journal of Geophysical Research C: Oceans | Year: 2015
Stratification and destratification processes in a tidally energetic, weakly stratified inlet in the Wadden Sea (south eastern North Sea) are investigated in this modeling study. Observations of current velocity and vertical density structure show strain-induced periodic stratification for the southern shoal of the tidal channel. In contrast to this, in the nearby central region of the channel, increased stratification is already observed directly after full flood. To investigate the processes leading to this different behavior, a nested model system using GETM is set up and successfully validated against field data. The simulated density development along a cross section that includes both stations shows that cross-channel stratification is strongly increasing during flood, such that available potential energy is released in the deeper part of the channel during flood. An analysis of the potential energy anomaly budget confirms that the early onset of vertical stratification during flood at the deeper station is mainly controlled by the stratifying cross-channel straining of the density field. In contrast to this, in the shallow part of the channel, the relatively weak cross-channel straining is balanced by along-channel straining and vertical mixing. An idealized analytical model confirms the following hypothesis: The laterally convergent flood current advecting laterally stratified water masses from the shallow and wide ebb tidal delta to the deep and narrow tidal channel has the tendency to substantially increase cross-channel density gradients in the tidal channel. This process leads to stratification during flood. © 2014. American Geophysical Union.
Van Opheusden B.,Leiden University |
Redig F.,Delft Institute of Applied Mathematics |
Schiessel H.,Leiden University
Journal of Physics A: Mathematical and Theoretical | Year: 2013
We study the dynamics of the nucleosome, the most abundant DNA protein complex in eukaryotic cells. The dynamics consist of two mechanisms, site exposure and sliding, which are crucial for making DNA accessible to DNA-binding proteins. The intertwining of both effects leads to a rich stochastic process that has not been studied before. Within the assumptions of our model, nucleosomes perform a symmetric random walk along the DNA strand. We investigate how the diffusion constant depends on the relative rates of site exposure and sliding. © 2013 IOP Publishing Ltd.
Raemaekers S.,Software Improvement Group |
Raemaekers S.,Technical University of Delft |
Nane G.F.,Delft Institute of Applied Mathematics |
Van Deursen A.,Technical University of Delft |
Visser J.,Software Improvement Group
IEEE International Working Conference on Mining Software Repositories | Year: 2013
Best practices in software development state that code that is likely to change should be encapsulated to localize possible modifications. In this paper, we investigate the application and effects of this design principle. We investigate the relationship between the stability, encapsulation and popularity of libraries on a dataset of 148,253 Java libraries. We find that bigger systems with more rework in existing methods have less stable interfaces and that bigger systems tend to encapsulate dependencies better. Additionally, there are a number of factors that are associated with change in library interfaces, such as rework in existing methods, system size, encapsulation of dependencies and the number of dependencies. We find that current encapsulation practices are not targeted at libraries that change the most. We also investigate the strength of ripple effects caused by instability of dependencies and we find that libraries cause ripple effects in systems using them and that these effects can be mitigated by encapsulation. © 2013 IEEE.
Van Gijzen M.B.,Delft Institute of Applied Mathematics |
Sonneveld P.,Delft Institute of Applied Mathematics
ACM Transactions on Mathematical Software | Year: 2011
The IDR(s) method that is proposed in Sonneveld and van Gijzen  is a very efficient limited memory method for solving large nonsymmetric systems of linear equations. IDR(s) is based on the induced dimension reduction theorem, that provides a way to construct subsequent residuals that lie in a sequence of shrinking subspaces. The IDR(s) algorithm that is given in Sonneveld and van Gijzen  is a direct translation of the theorem into an algorithm. This translation is not unique. This article derives a new IDR(s) variant, that imposes (one-sided) biorthogonalization conditions on the iteration vectors. The resulting method has lower overhead in vector operations than the original IDR(s) algorithms. In exact arithmetic, both algorithms give the same residual at every (s + 1)-st step, but the intermediate residuals and also the numerical properties differ. We show through numerical experiments that the new variant is more stable and more accurate than the original IDR(s) algorithm, and that it outperforms other state-of-the-art techniques for realistic test problems. © 2011 ACM 0098-3500/2011/11-ART5.
Cirillo P.,Delft Institute of Applied Mathematics |
Redig F.,Delft Institute of Applied Mathematics |
Ruszel W.,Delft Institute of Applied Mathematics
Journal of Physics A: Mathematical and Theoretical | Year: 2014
We analyze a class of energy and wealth redistribution models, characterizing their stationary measures and showing that they have a discrete dual process. In particular we show that the wealth distribution model with non-zero saving propensity can never have invariant product measures. We also introduce diffusion processes associated to the wealth distribution models by 'instantaneous thermalization'. © 2014 IOP Publishing Ltd.
van Horssen W.T.,Delft Institute of Applied Mathematics |
Pischanskyy O.V.,Delft Institute of Applied Mathematics |
Dubbeldam J.L.A.,Delft Institute of Applied Mathematics
Journal of Sound and Vibration | Year: 2010
In this paper the forced vibrations of a linear, single degree of freedom oscillator (sdofo) with a time-varying mass will be studied. The forced vibrations are due to small masses which are periodically hitting and leaving the oscillator with different velocities. Since these small masses stay for some time on the oscillator surface the effective mass of the oscillator will periodically vary in time. Additionally, an external harmonic force will be applied to the oscillator with a time-varying mass. Not only solutions of the oscillator equation will be constructed, but also stability properties for the forced vibrations will be presented for various parameter values. © 2009 Elsevier Ltd. All rights reserved.
Dubbeldam J.L.A.,Delft Institute of Applied Mathematics |
Rostiashvili V.G.,Max Planck Institute for Polymer Research |
Milchev A.,Max Planck Institute for Polymer Research |
Milchev A.,Bulgarian Academy of Science |
Vilgis T.A.,Max Planck Institute for Polymer Research
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2012
We suggest a theoretical description of the force-induced translocation dynamics of a polymer chain through a nanopore. Our consideration is based on the tensile (Pincus) blob picture of a pulled chain and the notion of a propagating front of tensile force along the chain backbone, suggested by Sakaue. The driving force is associated with a chemical potential gradient that acts on each chain segment inside the pore. Depending on its strength, different regimes of polymer motion (named after the typical chain conformation: trumpet, stem-trumpet, etc.) occur. Assuming that the local driving and drag forces are equal (i.e., in a quasistatic approximation), we derive an equation of motion for the tensile front position X(t). We show that the scaling law for the average translocation time τ changes from τ∼N2ν/f1 /ν to τ∼N1 +ν/f (for the free-draining case) as the dimensionless force f R=aNνf/T (where a, N, ν, f, and T are the Kuhn segment length, the chain length, the Flory exponent, the driving force, and the temperature, respectively) increases. These and other predictions are tested by molecular-dynamics simulation. Data from our computer experiment indicate indeed that the translocation scaling exponent α grows with the pulling force f R, albeit the observed exponent α stays systematically smaller than the theoretically predicted value. This might be associated with fluctuations that are neglected in the quasistatic approximation. © 2012 American Physical Society.