Recent Development of the Empirical Basis for Prediction of Vortex Induced Vibrations

This paper describes the research activity related to VIV that has taken place at NTNU and MARINTEK in Trondheim during the last years. The overall aim of the work has been increased understanding of the VIV phenomenon and to improve the empirical basis for prediction of VIV. The work has included experiments with flexible beams in sheared and uniform flow and forced motions of short, rigid cylinders. Key results in terms of hydrodynamic coefficients and analysis procedures have been implemented in the computer program VIVANA, which has resulted in new analysis options and improved hydrodynamic coefficients. Some examples of results are presented, but the main focus of the paper is to give an overview of the work and point out how the new results can be used in order to improve VIV analyses

Consolidation of Empirics for Calculation of VIV Response

The present paper consolidates available experimental results for both sub-critical and critical Reynolds numbers and varying surface roughness and formulates a coefficient excitation model that aims at unbiased response estimates when using semi-empirical VIV prediction programs. A simplified procedure is suggested to account for higher order effects when relevant. The paper discusses the use of a modified coefficient excitation model with the objective of capturing or correctly reflecting certain specific features that have been observed in sub-critical and supercritical VIV experiments. The first part of this paper shows how the available low Reynolds number hydrodynamic data that currently forms the basis for most semi-empirical prediction software needs to be modified to correctly reflect the available experimental observations at sub-critical Reynolds numbers. The latter part of this paper looks at the available high Reynolds experimental data and suggests ways whereby the previously identified force coefficient database might be modified to reflect what is currently known about the VIV response of smooth and rough surfaced cylinders in the critical and super-critical Reynolds regimes.Norway Deepwater Progra

OMAE2007-29172 DEEP WATER RISER COLLISION AVOIDANCE BY TOP TENSION CONTROL

ABSTRACT For tensioned riser arrays in deep waters interference between individual risers in strong ocean current is a key design and operational concern. The lateral deflections are likely to be large, and the risers may experience collision with fatigue or surface damage as a consequence. In this paper a system consisting of a tension leg platform (TLP), a pair of risers, environmental forces and hydrodynamic interaction is presented. The control system is described, and a set of control objectives with corresponding control strategies are suggested. The collision avoidance effects of the different control objectives are shown through simulations

Low-Velocity Halo Clouds

Models that reproduce the observed high-velocity clouds (HVCs) also predict clouds at lower radial velocities that may easily be confused with Galactic disk (|z| < 1 kpc) gas. We describe the first search for these low-velocity halo clouds (LVHCs) using IRAS data and the initial data from the Galactic Arecibo L-band Feed Array survey in HI (GALFA-HI). The technique is based upon the expectation that such clouds should, like HVCs, have very limited infrared thermal dust emission as compared to their HI column density. We describe our 'displacement-map' technique for robustly determining the dust-to-gas ratio of clouds and the associated errors that takes into account the significant scatter in the infrared flux from the Galactic disk gas. We find that there exist lower-velocity clouds that have extremely low dust-to-gas ratios, consistent with being in the Galactic halo - candidate LVHCs. We also confirm the lack of dust in many HVCs with the notable exception of complex M, which we consider to be the first detection of warm dust in HVCs. We do not confirm the previously reported detection of dust in complex C. In addition, we find that most Intermediate- and Low-Velocity clouds that are part of the Galactic disk have a higher 60 micron/100 micron flux ratio than is typically seen in Galactic HI, which is consistent with a previously proposed picture in which fast-moving Galactic clouds have smaller, hotter dust grains.Comment: 30 pages, 7 figures. Accepted to the Ap

The Procedural Index for Mortality Risk (PIMR): an index calculated using administrative data to quantify the independent influence of procedures on risk of hospital death

<p>Abstract</p> <p>Background</p> <p>Surgeries and other procedures can influence the risk of death in hospital. All published scales that predict post-operative death risk require clinical data and cannot be measured using administrative data alone. This study derived and internally validated an index that can be calculated using administrative data to quantify the independent risk of hospital death after a procedure.</p> <p>Methods</p> <p>For all patients admitted to a single academic centre between 2004 and 2009, we estimated the risk of all-cause death using the Kaiser Permanente Inpatient Risk Adjustment Methodology (KP-IRAM). We determined whether each patient underwent one of 503 commonly performed therapeutic procedures using Canadian Classification of Interventions codes and whether each procedure was emergent or elective. Multivariate logistic regression modeling was used to measure the association of each procedure-urgency combination with death in hospital independent of the KP-IRAM risk of death. The final model was modified into a scoring system to quantify the independent influence each procedure had on the risk of death in hospital.</p> <p>Results</p> <p>275 460 hospitalizations were included (137,730 derivation, 137,730 validation). In the derivation group, the median expected risk of death was 0.1% (IQR 0.01%-1.4%) with 4013 (2.9%) dying during the hospitalization. 56 distinct procedure-urgency combinations entered our final model resulting in a Procedural Index for Mortality Rating (PIMR) score values ranging from -7 to +11. In the validation group, the PIMR score significantly predicted the risk of death by itself (c-statistic 67.3%, 95% CI 66.6-68.0%) and when added to the KP-IRAM model (c-index improved significantly from 0.929 to 0.938).</p> <p>Conclusions</p> <p>We derived and internally validated an index that uses administrative data to quantify the independent association of a broad range of therapeutic procedures with risk of death in hospital. This scale will improve risk adjustment when administrative data are used for analyses.</p

In Situ Observations of the Deformation Behavior and Fracture Mechanisms of Ti-45Al-2Nb-2Mn+0.8 vol pct TiB₂

The deformation and fracture mechanisms of a nearly lamellar Ti-45Al-2Nb-2Mn (at. pct) + 0.8 vol pct TiB₂ intermetallic, processed into an actual low-pressure turbine blade, were examined by means of in situ tensile and tensile-creep experiments performed inside a scanning electron microscope (SEM). Low elongation-to-failure and brittle fracture were observed at room temperature, while the larger elongations-to-failure at high temperature facilitated the observation of the onset and propagation of damage. It was found that the dominant damage mechanisms at high temperature depended on the applied stress level. Interlamellar cracking was observed only above 390 MPa, which suggests that there is a threshold below which this mechanism is inhibited. Failure during creep tests at 250 MPa was controlled by intercolony cracking. The in situ observations demonstrated that the colony boundaries are damage nucleation and propagation sites during tensile creep, and they seem to be the weakest link in the microstructure for the tertiary creep stage. Therefore, it is proposed that interlamellar areas are critical zones for fracture at higher stresses, whereas lower stress, high-temperature creep conditions lead to intercolony cracking and fracture.The authors are grateful to Industria de Turbo Propulsores, S.A. for supplying the intermetallic blades. Funding from the Spanish Ministry of Science and Innovation through projects MAT2009-14547-C02-01 and MAT2009-14547-C02-02 is acknowledged. The Madrid Regional Government supported this project partially through the ESTRUMAT grant P2009/MAT-1585. C.J.B. acknowledges the support from Grant SAB2009-0045 from the Spanish Ministry of Education for his sabbatical stage in Madrid.Publicad

Global Expression Profiling in Atopic Eczema Reveals Reciprocal Expression of Inflammatory and Lipid Genes

Atopic eczema (AE) is a common chronic inflammatory skin disorder. In order to dissect the genetic background several linkage and genetic association studies have been performed. Yet very little is known about specific genes involved in this complex skin disease, and the underlying molecular mechanisms are not fully understood.We used human DNA microarrays to identify a molecular picture of the programmed responses of the human genome to AE. The transcriptional program was analyzed in skin biopsy samples from lesional and patch-tested skin from AE patients sensitized to Malassezia sympodialis (M. sympodialis), and corresponding biopsies from healthy individuals. The most notable feature of the global gene-expression pattern observed in AE skin was a reciprocal expression of induced inflammatory genes and repressed lipid metabolism genes. The overall transcriptional response in M. sympodialis patch-tested AE skin was similar to the gene-expression signature identified in lesional AE skin. In the constellation of genes differentially expressed in AE skin compared to healthy control skin, we have identified several potential susceptibility genes that may play a critical role in the pathological condition of AE. Many of these genes, including genes with a role in immune responses, lipid homeostasis, and epidermal differentiation, are localized on chromosomal regions previously linked to AE.Through genome-wide expression profiling, we were able to discover a distinct reciprocal expression pattern of induced inflammatory genes and repressed lipid metabolism genes in skin from AE patients. We found a significant enrichment of differentially expressed genes in AE with cytobands associated to the disease, and furthermore new chromosomal regions were found that could potentially guide future region-specific linkage mapping in AE. The full data set is available at http://microarray-pubs.stanford.edu/eczema