A reduced order data assimilation scheme coupled with a two-way nested model. Application to the Ligurian Sea

Conference (2004, April)

A system of nested models is coupled with a data assimilation module. The system is composed by a low resolution model (1/4 ) covering the whole Mediterranean Sea, an intermediate resolution model (1/20 ... [more ▼]

A system of nested models is coupled with a data assimilation module. The system is composed by a low resolution model (1/4 ) covering the whole Mediterranean Sea, an intermediate resolution model (1/20 ) of the Liguro-Provençal basin and a high resolution model (1/60 ) simulating the fine mesoscale structures in the Ligurian Sea. Boundary conditions and the averaged fields (feedback) are exchanged between two successive nesting levels. A reduced order, optimal interpolation data assimilation scheme was implemented. The state vector is composed by temperature, salinity and sea surface elevation. Novel in the present approach is that these variables from the three nested model grids are assembled to one multigrid state vector. This implementation allows to take into account the correlation of the variables across the nested model grids in order to avoid for example artificial gradients after an assimilation cycle. The eigenvectors of the covariance matrix are constructed by an EOF analysis of the free model run. Cross-grid correlations especially in the overlapping domains are thus consistently represented. Horizontal correlations over long distances are suppressed by multiplying each error mode with a set of radial Gaussian functions. This procedure increases considerably the rank of the covariance matrix but ensures the local impact of each observation. Sea surface temperature (SST, from the DLR EOWEB), sea surface height (SSH, from the CLS) and CTD profiles (SIRENA cruise from SACLANT Center and cruises from the MEDAR/Medatlas database) are assimilated into the model. In overlapping model grids the measurements are related to the highest resolution grid. Since the SSH has a resolution of 1/8 , the surface elevation of the Ligurian Sea and the Liguro-Provençal model are filtered in order to be coherent with the space scales present in the observations. Starting from the 1st January 1998 the low and intermediate resolution models are spun up for 18 months. The initial conditions for the Ligurian Sea are interpolated from the intermediate resolution model. The three models are then integrated until August 1999. During this period SST, SSH and the CTD profiles are assimilated. The results are compared with a free model run. In particular the model forecast just before the assimilation step are compared with the observations. The model forecast and the measurements are then independent and the difference is a measure of the model forecast skill and the impact of the previous assimilation cycles. [less ▲]

Reduced organ failure with effective glycemic control

in Intensive Care Medicine (2010), 36(2), 173-173

Reduced proviral loads during primo-infection of sheep by Bovine Leukemia virus attenuated mutants.

in Retrovirology (2004), 1(1),

Reduced Slow-Wave Rebound during Daytime Recovery Sleep in Middle-Aged Subjects

in PLoS ONE (2012), 7(8), 43224

Reduced Sperm Counts In Guppies (Poecilia Reticulata) Following Exposure To Low Levels Of Tributyltin And Bisphenol A

in Proceedings of the Royal Society B-Biological Sciences (2000), 267(1459),

A reduced-gravity model for the Catalan Sea

in Journal of Marine Systems (1991), 4

Reduced-order modeling of electrostatically-actuated micro-beams

in Proceedings of the 6th EUROMECH Nonlinear Dynamics Conference (ENOC) (2008)

This paper addresses the compact modeling of MEMS devices with nonlinear electromechanical forces. Ideally, the reduced-order model should only involve one or two generalized coordinates. We show that a ... [more ▼]

This paper addresses the compact modeling of MEMS devices with nonlinear electromechanical forces. Ideally, the reduced-order model should only involve one or two generalized coordinates. We show that a projection method based on the first eigenmode of the linearized unactuated structure is a good choice in terms of simplicity and accuracy. To take into account the influence of distributed electrostatic forces, it is necessary to approximate the nonlinear force in terms of the reduced coordinate. It is shown that a Pad´e approximation of order 2 is very attractive in terms of accuracy and numerical efficiency. [less ▲]

Reduced-order modeling of flexible mechanisms with configuration-dependent dynamics: a modal approach

Conference (2005, September)

Modern formalisms in multibody dynamics allow a detailed and reliable representation of complex mechanical systems. However, high levels of accuracy and generality can only be reached at the price of more ... [more ▼]

Modern formalisms in multibody dynamics allow a detailed and reliable representation of complex mechanical systems. However, high levels of accuracy and generality can only be reached at the price of more sophisticated models, which require increased computational resources. Reduction techniques have thus been developed in order to build simplified models able to capture the essential dynamics of a flexible mechanism. In this talk, a methodology is proposed to transform an initial high-order Finite Element model into a low-order and explicit model. The reduction method is an extension of the component-mode technique established in linear structural dynamics, which accounts for the nonlinear kinematics of the mechanism. It relies on the original concept of “Global Modal Parameterization”: the motion of the assembled mechanism is described in terms of rigid and flexible modes, which depend on the mechanical configuration. We will show that the reduction procedure leads to a consistent model, with configuration-dependent parameters. The nonlinear variations of those parameters are approximated using a piecewise polynomial interpolation. This strategy is based on an adaptive configuration space inspection algorithm, which minimizes the computational resources to satisfy a specification on the approximation error. Several examples will be considered in the presentation: a four-bar mechanism, a parallel kinematic machine-tool, and a lightweight manipulator. [less ▲]

Reducing hazards for humans from animals: emerging and re-emerging zoonoses

in Italian Journal of Public Health (2012), 9(2), 13-24

Reducing leg oedema after femoro-popliteal bypass surgery: a challenge.

in European Journal of Vascular and Endovascular Surgery (2010), 40(5), 643-4