Objective multiscale analysis of random heterogeneous materials

The multiscale framework presented in [1, 2] is assessed in this contribution for a study of random heterogeneous materials. Results are compared to direct numerical simulations (DNS) and the sensitivity to user-defined parameters such as the domain decomposition type and initial coarse scale resolution is reported. The parallel performance of the implementation is studied for different domain decompositions

Prediction of Instability in Rotor-Seal Systems using Forward Whirl Magnetic Bearing Excitation

To separate different fluids and pressure levels in high-speed turbomachinery or pumps, mostly contactless seals are used. The leakage flow inside the seal gap applies forces to the vibrating rotor system in deflectional and tangential directions, that are dependent on the rotational speed. Above a speed limit, mainly tangential seal forces can lead to self-excited vibrations and, ultimately, rotor instability. This is similar to the “oil whip” phenomenon in journal bearings. To predict the speed limit, two methods are shown and compared: Simulations based on the bulk flow assumptions and an experimental method. To demonstrate the application, a test rig is used. The experimental method uses measured transfer functions, utilizing an active magnetic bearing for forward whirl excitation in the safe operational range. The speed limit can be predicted by analyzing and extrapolating the vibrational behavior of the rotor-seal system

Simulation and Experimental Validation of a Misaligned Rotor in Journal Bearings using Different Levels of Detail

In this contribution, a given test rig of a rotor system with journal bearing is validated by using simulation models with different levels of detail. A special focus is placed on the misalignment between rotor and bearing axis. It is shown, how to consider misalignment in the numeric calculation of the bearing forces as well as in the modeling of the rotor system. With a model of the LAVAL rotor, the misalignment in the test rig is identified by measuring and simulating relative equilibrium positions of the rotor in the bearing at different rotational speeds. A measured rotor orbit due to unbalance is used to compare simulation results of different complex rotor models and discuss their accuracy and efficiency

BDDC and FETI-DP under Minimalist Assumptions

The FETI-DP, BDDC and P-FETI-DP preconditioners are derived in a particulary simple abstract form. It is shown that their properties can be obtained from only on a very small set of algebraic assumptions. The presentation is purely algebraic and it does not use any particular definition of method components, such as substructures and coarse degrees of freedom. It is then shown that P-FETI-DP and BDDC are in fact the same. The FETI-DP and the BDDC preconditioned operators are of the same algebraic form, and the standard condition number bound carries over to arbitrary abstract operators of this form. The equality of eigenvalues of BDDC and FETI-DP also holds in the minimalist abstract setting. The abstract framework is explained on a standard substructuring example.Comment: 11 pages, 1 figure, also available at http://www-math.cudenver.edu/ccm/reports

Protocol for a randomized controlled trial on risk adapted damage control orthopedic surgery of femur shaft fractures in multiple trauma patients

<p>Abstract</p> <p>Background</p> <p>Fractures of the long bones and femur fractures in particular are common in multiple trauma patients, but the optimal management of femur fractures in these patients is not yet resolved. Although there is a trend towards the concept of "Damage Control Orthopedics" (DCO) in the management of multiple trauma patients with long bone fractures as reflected by a significant increase in primary external fixation of femur fractures, current literature is insufficient. Thus, in the era of "evidence-based medicine", there is the need for a more specific, clarifying trial.</p> <p>Methods/Design</p> <p>The trial is designed as a randomized controlled open-label multicenter study. Multiple trauma patients with femur shaft fractures and a calculated probability of death between 20 and 60% will be randomized to either temporary fracture fixation with fixateur externe and defined secondary definitive treatment (DCO) or primary reamed nailing (early total care). The primary objective is to reduce the extent of organ failure as measured by the maximum sepsis-related organ failure assessment (SOFA) score.</p> <p>Discussion</p> <p>The Damage Control Study is the first to evaluate the risk adapted damage control orthopedic surgery concept of femur shaft fractures in multiple trauma patients in a randomized controlled design. The trial investigates the differences in clinical outcome of two currently accepted different ways of treating multiple trauma patients with femoral shaft fractures. This study will help to answer the question whether the "early total care" or the „damage control” concept is associated with better outcome.</p> <p>Trial registration</p> <p>Current Controlled Trials ISRCTN10321620</p

Application of the FETI Method to ASCI Problems: Scalability Results on a Thousand-Processors and Discussion of Highly Heterogeneous Problems

We report on the application of the one-level FETI method to the solution of a class of structural problems associated with the Department of Energy's Accelerated Strategic Computing Initiative (ASCI). We focus on numerical and parallel scalability issues,and discuss the treatment by FETI of severe structural heterogeneities. We also report on preliminary performance results obtained on the ASCI Option Red supercomputer configured with as many as one thousand processors, for problems with as many as 5 million degrees of freedom