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

Noise estimation of beveled trailing edges using an integral and boundary element method

Numerical simulations involving multiple, physically different domains can be solved effectively by coupling simulation programs, or solvers. The coordination of the different solvers is commonly handled by a coupling shell. A coupling shell synchronizes the execution of the solvers and handles the transfer of data from one physical domain to another. In this paper, we introduce Flecs, a flexible coupling shell, designed for implementing and applying an interface for multidisciplinary simulations with superior accuracy. The aim is not to achieve the best possible efficiency or to support a large feature set, but to provide a flexible platform for developing new data transfer algorithms and coupling schemes.

/pdf/flecs-a-flexible-coupling-shell-application-to-fluid-27mzy968li.pdf

Flecs, a flexible coupling shell application to fluid-structure interaction

Multi-physics simulations, such as fluid-structure-acoustics interaction (FSA), require a high performance computing environment in order to perform the simulation in a reasonable amount of computation time. Currently used coupling methods use a staggered execution of the fluid and solid solver [6], which leads to inherent load imbalances. In [12] a new coupling scheme based on a quasi-Newton method is proposed for fluidstructure interaction which coupled the fluid and solid solver in parallel. The quasi-Newton method requires approximately the same number of coupling iterations per time step compared to a staggered coupling approach, resulting in a better load balance when running in a parallel environment. This contribution investigates the scalability limit and load-balancing for a strongly coupled fluid-structure interaction problem, and also for a fluid-structure-acoustics interaction problem. The acoustic far field of the fluid-structure-acoustics interaction problem is loosely coupled with the flow field.

/pdf/on-parallel-scalability-aspects-of-strongly-coupled-y4hxlmyvcm.pdf

On parallel scalability aspects of strongly coupled partitioned fluid-structure-acoustics interaction

Strongly coupled fluid-structure interaction simulations often suffer from slow convergence, limited parallel scalability or difficulties in using black-box solvers. As partitioned simulations still play an important role in cases where new combinations of models, discretizations and codes have to be tested in an easy and fast way, we propose a combination of a parallel black-box coupling with a manifold mapping algorithm as an acceleration method. In this approach, we combine a computationally inexpensive low-fidelity FSI model with a high-fidelity FSI model to reduce the number of coupling iterations of the high fidelity FSI model. Information from previous time steps is taken into account with a secant update step similar to the Broyden update. The used black-box approach is applied for an incompressible laminar flow over a fixed cylinder with an attached flexible flap and a wave propagation in a three-dimensional elastic tube problem. A reduction of approximately 55 % in terms of high fidelity iterations is achieved compared to the Anderson mixing method if the fluid and the structure solvers are executed in parallel.

Multi-Level Acceleration of Parallel Coupled Partitioned Fluid-Structure Interaction with Manifold Mapping

Methods for solving the discretized equations of uid motion are discussed, with particular reference to ecient methods for solving compressible ow problems to a steady state. A spectrum of algorithms of widely varying eciency and complexity are considered, from explicit single-stage methods, through Runge-Kutta, implicit methods, defect correction, to multigrid. They are classied with respect to cost per iteration, convergence rate and memory requirements, and compared for a concrete high-Reynolds number test-case. Time-resolved calculations are then considered using the dual-time framework.

Hester Bijl

Papers

Noise estimation of beveled trailing edges using an integral and boundary element method

Flecs, a flexible coupling shell application to fluid-structure interaction

On parallel scalability aspects of strongly coupled partitioned fluid-structure-acoustics interaction

Multi-Level Acceleration of Parallel Coupled Partitioned Fluid-Structure Interaction with Manifold Mapping

Solution methods and acceleration techniques in CFD