191,577 research outputs found
Koopman-SPCL
No full text的动态演化规律PM2.5并准确预测，对于公共卫生管理和预警决策活动的实施具有重要意义。本研究利用Koopman算子的谱特性来解释复数PM2.5的内在演化规律并利用深度学习实现从非线性状态空间到Koopman不变子空间的映射，以考虑直线距离PM2.5关系状态空间转换期间的站点。本研究揭示了PM2.5不同尺度上呈现出时空变化规律，对本文具有重要意义。该研究还阐明PM2.5 复杂非线性动力系统解释性质。</p
Global and Koopman modes analysis of sound generation in mixing layers
No full textIt is now well established that linear and nonlinear instability waves play a significant role in the noise generation process for a wide variety of shear flows such as jets or mixing layers. In that context, the problem of acoustic radiation generated by spatially growing instability waves of two-dimensional subsonic and supersonic mixing layers are revisited in a global point of view, i.e., without any assumption about the base flow, in both a linear and a nonlinear framework by using global and Koopman mode decompositions. In that respect, a timestepping technique based on disturbance equations is employed to extract the most dynamically relevant coherent structures for both linear and nonlinear regimes. The present analysis proposes thus a general strategy for analysing the near-field coherent structures which are responsible for the acoustic noise in these configurations. In particular, we illustrate the failure of linear global modes to describe the noise generation mechanism associated with the vortex pairing for the subsonic regime whereas they appropriately explain the Mach wave radiation of instability waves in the supersonic regime. By contrast, the Dynamic Mode Decomposition (DMD) analysis captures both the near-field dynamics and the far-field acoustics with a few number of modes for both configurations. In addition, the combination of DMD and linear global modes analyses provides new insight about the influence on the radiated noise of nonlinear interactions and saturation of instability waves as well as their interaction with the mean flow
Koopman-based Model Predictive Control of quadrotors
No full textA novel formulation of model predictive control (MPC) coupled with Koopman operator theory is presented and tested for the trajectory tracking problem of a quadrotor UAV. The analytical derivation of Koopman observables allows for the quadrotor model to be written as a fully-actuated quasi-linear system which enables the control problem to be posed as a linear control problem. In fact, the adopted approach embeds the quadrotor nonlinear dynamics into a quasi-linear form through the evolution of the Koopman op-erator generalized eigenfunctions, a special kind of Koopman observables. Hence, the linear MPC formulation in Koopman coordinates is equivalent to a nonlinear implementation in the original state space. Moreover, in an enhancement from the standard feedback linearization, the Koopman based quadro-tor model does not present underactuation, which drastically simplifies the computational requirement for the solution of the MPC optimization problem. The presented methodology is tested through detailed numerical simulations and results are compared to single-loop nonlinear MPC (NMPC). The satisfactory tracking performance are additionally enhanced by the obtained computational speedup which is crucial for real time implementation of flight controllers
Kinderen met downsyndroom Passend Onderwijs
No full textIn dit onderzoek wordt verslag gedaan van een onderzoek dat onderdeel is van het landelijke evaluatieprogramma passend onderwijs. Dit evaluatieprogramma wordt gefinancierd door het Nationaal Regieorgaan Onderwijsonderzoek (NRO). Het betreft een onderzoek dat uitgevoerd is op verzoek van het Ministerie van Onderwijs, Cultuur & Wetenschap en is uitgevoerd in samenwerking met Stichting Downsyndroom (SDS). Het doel van dit onderzoek is duidelijkheid te geven over de positie van kinderen met Downsyndroom in de periode van het primair onderwijs en de overgang naar het voorgezet onderwijs, voor en na passend onderwijs.
Bestanden:
Rapport:
"Kinderen met Downsyndroom in het onderwijs.pdf"
Koopman, P.N.J., Eck, P. van, & Boer, A. de.
M.m.v. Bomhof, M., Exalto, R., Graaf, G. de, Ledoux, G.
Kinderen met Downsyndroom in het onderwijs. Periode 2008/09 – 2017/18.
Utrecht: Oberon, Amsterdam: Kohnstamm Instituut.
Dit is publicatie nr. 42 in de reeks Evaluatie Passend Onderwijs.
ISBN:978-94-6321-060-7
Vragenlijst:
"Vragenlijst Leerlingen met DS in passend onderwijs_Anker en Monitorvragen_15012017.pdf"
Spss dataset:
"Analysebestand_vragenlijstSvD.sav"
Why functional programming matters to me
No full textContains fulltext :
120060.pdf (Publisher’s version ) (Open Access
Koopman analysis of Burgers equation
No full textThe emergence of dynamic mode decomposition (DMD) as a practical way to attempt a Koopman mode decomposition of a nonlinear partial differential equation (PDE) presents exciting prospects for identifying invariant sets and slowly decaying transient structures buried in the PDE dynamics. However, there are many subtleties in connecting DMD to Koopman analysis, and it remains unclear how realistic Koopman analysis is for complex systems such as the Navier-Stokes equations. With this as motivation, we present here a full Koopman decomposition for the velocity field in the Burgers equation by deriving explicit expressions for the Koopman modes and eigenfunctions. As far as we are aware the first time this has been done for a nonlinear PDE. The decomposition highlights the fact that different observables can require different subsets of Koopman eigenfunctions to express them, and it presents a nice example in which (i) the Koopman modes are linearly dependent and so they cannot be fit a posteriori to snapshots of the flow without knowledge of the Koopman eigenfunctions, and (ii) the Koopman eigenvalues are highly degenerate, which means that computed Koopman modes become initial-condition-dependent. As a way of illustration, we discuss the form of the Koopman expansion with various initial conditions, and we assess the capability of DMD to extract the decaying nonlinear coherent structures in run-down simulations.</p
Koopman analysis of isolated fronts and solitons
No full textA Koopman decomposition of a complex system leads to a representation in
which nonlinear dynamics appear to be linear. The existence of a linear
framework with which to analyse nonlinear dynamical systems brings new
strategies for prediction and control, while the approach is straight-forward
to apply to large datasets owing to a connection with dynamic mode
decomposition (DMD). However, it can be challenging to connect the output of
DMD to a Koopman analysis since there are relatively few analytical results
available, while the DMD algorithm itself is known to struggle in situations
involving the propagation of a localised structure through the domain.
Motivated by these issues, we derive a series of Koopman decompositions for
localised, finite-amplitude solutions of classical nonlinear PDEs. We first
demonstrate that nonlinear travelling wave solutions to both the Burgers and
KdV equations have two Koopman decompositions; one of which converges upstream
and another which converges the other downstream of the soliton or front. We
then use the inverse scattering transform to derive a full Koopman
decomposition for (pure soliton) solutions to the KdV equation, identifying
Koopman eigenvalues, eigenfunctions and modes. Our analysis indicates that
there are many possible Koopman decompositions when the solution involves the
interaction of multiple solitons. The existence of multiple expansions in space
and time has a critical impact on the ability of DMD to extract Koopman
eigenvalues and modes - which must be performed within a temporally and
spatially localised window to correctly identify the separate expansions. In
addition, we provide evidence that these features may be generic for isolated
nonlinear structures by applying DMD to a moving breather solution of the
sine-Gordon equation
Koopman Operator Based Modeling and Control of Quadrotors
No full textA novel set of Koopman observables is introduced to transform the nonlinear quadrotor dynamics into a linear representation. The proposed approach is a combination of feedback linearization and Koopman observables, and it offers the advantage of overcoming the quadrotor underactuation problem. Compared to previous approaches that use dynamic inversion for both position and attitude dynamics, in this work, only the attitude dynamics are feedback linearized. The formulation is shown to be considerably more compact and capable of achieving lower model mismatch error when compared to already published similar work. The advantage of this formulation is that it allows for designing control architectures exploiting well-known linear control theory. As such, a Koopman based linear quadratic (LQ) controller is tested via numerical simulations to show applicability and implementability of the approach
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