다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Statistics for Spatial Data.

The purpose of this paper is to provide a comprehensive presentation and interpretation of the Ensemble Kalman Filter (EnKF) and its numerical implementation. The EnKF has a large user group, and numerous publications have discussed applications and theoretical aspects of it. This paper reviews the important results from these studies and also presents new ideas and alternative interpretations which further explain the success of the EnKF. In addition to providing the theoretical framework needed for using the EnKF, there is also a focus on the algorithmic formulation and optimal numerical implementation. A program listing is given for some of the key subroutines. The paper also touches upon specific issues such as the use of nonlinear measurements, in situ profiles of temperature and salinity, and data which are available with high frequency in time. An ensemble based optimal interpolation (EnOI) scheme is presented as a cost-effective approach which may serve as an alternative to the EnKF in some applications. A fairly extensive discussion is devoted to the use of time correlated model errors and the estimation of model bias.

The Ensemble Kalman Filter: Theoretical formulation and practical implementation

Adaptive sparse polynomial chaos expansion based on least angle regression

To improve the performance of particle image velocimetry in measuring instantaneous velocity fields, direct cross-correlation of image fields can be used in place of auto-correlation methods of interrogation of double- or multiple-exposure recordings. With improved speed of photographic recording and increased resolution of video array detectors, cross-correlation methods of interrogation of successive single-exposure frames can be used to measure the separation of pairs of particle images between successive frames. By knowing the extent of image shifting used in a multiple-exposure and by a priori knowledge of the mean flow-field, the cross-correlation of different sized interrogation spots with known separation can be optimized in terms of spatial resolution, detection rate, accuracy and reliability.

Theory of cross-correlation analysis of PIV images : Image analysis as measuring technique in flows

In this paper an efficient framework for uncertainty quantification in computational fluid dynamics is presented. Geometrical uncertainties are efficienty treated by using a mesh deformation technique and multiple uncertainties are propagated using a Two-Step approach. Both steps are performed using the Probabilistic Collocation method. The first step consists of a sensitivity analysis to identify the most important parameters of the problem. The sensitivity derivatives are obtained using a first or second order Probabilistic Collocation approximation. For the most important parameters the probability distribution functions are propagated using the Probabilistic Collocation method using higher order approximations. The Two-Step approach is demonstrated for flow around a NACA0012 airfoil with eight uncertain parameters in the free stream conditions and geometry. To efficiently handle geometrical uncertainties, a mesh deformation algorithm was employed. This avoids remeshing for every collocation point. The first step identified the freestream velocity, angle of attack, and the camber of the airfoil as the three most important parameters. In the second step the probability distributions of all three parameters are propagated using higher order Probabilistic Collocation approximations. Statistical properties of the lift and drag are obtained, as well as uncertainty bounds for the pressure and skinfriction on the surface of the airfoil.

An Efficient Framework for Uncertainty Quantification in CFD using Probabilistic Collocation.

High computational cost associated with the high fidelity wake models such as RANS or LES serves as a primary bottleneck to perform a direct high fidelity wind farm layout optimization (WFLO) using accurate CFD based wake models. Therefore, a surrogate based multi-fidelity WFLO methodology (SWFLO) is proposed. The surrogate model is built using an SBO method referred as manifold mapping (MM). As a verification, optimization of spacing between two staggered wind turbines was performed using the proposed surrogate based methodology and the performance was compared with that of direct optimization using high fidelity model. Significant reduction in computational cost was achieved using MM: a maximum computational cost reduction of 65%, while arriving at the same optima as that of direct high fidelity optimization. The similarity between the response of models, the number of mapping points and its position, highly influences the computational efficiency of the proposed method. As a proof of concept, realistic WFLO of a small 7-turbine wind farm is performed using the proposed surrogate based methodology. Two variants of Jensen wake model with different decay coefficients were used as the fine and coarse model. The proposed SWFLO method arrived at the same optima as that of the fine model with very less number of fine model simulations.

http://iopscience.iop.org/article/10.1088/1742-6596/753/9/092005/pdf

Surrogate based wind farm layout optimization using manifold mapping

We present an integrated in-situ visualization approach for partitioned multi-physics simulation of fluid-structure interaction. The simulation itself is treated as a black box and only the information at the fluid-structure interface is considered, and communicated between the fluid and solid solvers with a separate coupling tool. The visualization of the interface data is performed in conjunction with the fluid solver. Furthermore, we present new visualization techniques for the analysis of the interrelation of the two solvers , with emphasis on the involved error due to discretization in space and time and the reconstruction. Our visualization approach also enables the investigation of these errors with respect of their mutual influence on the two simulation codes and their space-time discretization. For efficient interactive visualization, we employ the concept of explorable spatiotemporal images, which also enables finite-time temporal navigation in an in-situ context. We demonstrate our overall approach and its utility by means of a fluid-structure simulation using OpenFOAM that is coupled by the preCICE software layer.

/pdf/on-in-situ-visualization-for-strongly-coupled-partitioned-2213izdqkw.pdf

On in-situ visualization for strongly coupled partitioned fluid-structure interaction

Mesh adaptation is a fairly established tool to obtain numerically ac- curate solutions for flow problems. Computational efficiency is, however, not al- ways guaranteed for the adaptation strategies found in literature. Typically exces- sive mesh growth diminishes the potential efficiency gain. This paper, therefore, extends the strategy proposed by (Aftosmis and Berger (2002)) to compute the re- finement threshold. The extended strategy computes the refinement threshold based on a user desired number of grid cells and adaptations, thereby ensuring high com- putational efficiency. Because our main interest is flow around wind turbines, the adaptation strategy has been optimized for flow around wind turbine airfoils. The proposed strategy was found to yield computationally efficient computations for flow around wind turbine airfoils as well as for other flow problems.

An automated approach for solution based mesh adaptation to enhance numerical accuracy for a given number of grid cells \\ \emph {Applied to steady flow on hexahedral grids}

Hester Bijl

Papers

An Efficient Framework for Uncertainty Quantification in CFD using Probabilistic Collocation.

Surrogate based wind farm layout optimization using manifold mapping

On in-situ visualization for strongly coupled partitioned fluid-structure interaction

An automated approach for solution based mesh adaptation to enhance numerical accuracy for a given number of grid cells \\ \emph {Applied to steady flow on hexahedral grids}

Numerical and experimental analysis of tandem flapping flight