65 research outputs found
Numerical Investigation of the Influence of Span-wise Force Variation in Circular Cylinders Undergoing Vortex Induced Vibrations at High Reynolds Number
The focus of this research is on the development
of a new approach for simulating vortex induced vibrations on
marine risers at high Reynolds numbers. This method considers
the span-wise variation of the lift and drag forces, and determines
the moment acting on the cylinder. The predicted motion then
consists of a rotational component to accompany the traditional
cross-stream and stream-wise translations normally associated
with vortex induced vibrations. This was accomplished by describing
the motion of the cylinder using a set of springs and
dampers. A moment acting on the cylinder causes the springs on
one end to compress, and stretch on the other, thus rotating the
cylinder.
A Large Eddy Simulation (LES) computational fluid dynamics
code running on 16 3Ghz processors was used to calculate the
unsteady flow and at each time step the hydrodynamic forces
acting on the cylinder were calculated in a separate routine based
on the pressure distribution around the cylinder. This information
was then used to solve two second-order ordinary differential
equations, which gave the velocity and displacement of the
cylinder in cross-flow and rotational planes. This information was
transferred back to the code where the cylinder was displaced
and another cycle of calculations was started.
The simulated results showed that the correlation length was
higher for a cylinder subject to pure translation compared to a
cylinder free to translate and rotate in the cross-stream direction.
This has implications for current numerical and experimental
techniques since it has been traditionally assumed that the
flow around a circular cylinder becomes two-dimensional during
vortex induced vibrations. Consequently, empirical,numerical
and experimental models have generally only considered cross
stream and/or stream-wise translation. The extent to which the
experimental apparatus or harmonic model may have influenced
the behavior of the riser by eliminating span-wise amplitude
variation is important information that should be considered for
future riser designs
NUMERICAL ANALYSIS OF THE NATURAL CONVECTION IN HORIZONTAL ANNULI AT LOW AND MODERATE Ra
The natural convection at low and moderate Rayleigh numbers (Ra) incylindrical horizontal annuli with imposed temperatures in both surfaces isnumerically studied. This flow inside concentric cylinders classic configuration has a wide range of practical and technological applications, which justifies its growing studies efforts. In this work, the governing equations are discretized by the volume finite technique over a staggered grid, with second-order accuracy in space and time. The flow pattern is presented by several Rayleigh numbers, with an analysis of the heat transfer coefficient and flow properties. Furthermore, a three-dimensional field is shown at a moderate Ra number. The results showed a good agreement with the experimental data
Treatment change as a predictor of outcome among patients with classic chronic graft-versus-host disease
We analyzed outcomes for 668 patients who had systemic treatment for chronic graft-versus-host disease (GVHD) to assess the utility of early treatment change for exacerbation of chronic GVHD as a surrogate for survival endpoints in clinical trials. Fifty-six percent of patients had treatment change within 2 years after diagnosis of chronic GVHD. The median onset of treatment change was 4.4 months (range, 0.3 – 50 months). The cumulative incidence of non-relapse mortality (NRM) at 2 years was 16%, and overall survival at 2 years was 74%. In time-dependent Cox models, treatment change was associated with an increase in risk of NRM (hazard ratio, 2.53; 95% CI, 1.7-3.7; p < .0001). The hazard ratio was attenuated by 6% per month of delay in treatment change. Our results confirm that exacerbation of chronic GVHD is associated with an increased risk of NRM and with decreased survival, but the strength of this association is not large enough to allow the use of early exacerbation as a surrogate for survival endpoints in clinical trials. Other measures of clinical benefit, such as response, will need to be developed as endpoints in phase II trials for patients with chronic GVHD
The inflammatory microenvironment in colorectal neoplasia
Peer reviewedPublisher PD
ILC3 function as a double-edged sword in inflammatory bowel diseases
Inflammatory bowel diseases (IBD), composed mainly of Crohn’s disease (CD) and ulcerative colitis (UC), are strongly implicated in the development of intestinal inflammation lesions. Its exact etiology and pathogenesis are still undetermined. Recently accumulating evidence supports that group 3 innate lymphoid cells (ILC3) are responsible for gastrointestinal mucosal homeostasis through moderate generation of IL-22, IL-17, and GM-CSF in the physiological state. ILC3 contribute to the progression and aggravation of IBD while both IL-22 and IL-17, along with IFN-γ, are overexpressed by the dysregulation of NCR− ILC3 or NCR+ ILC3 function and the bias of NCR+ ILC3 towards ILC1 as well as regulatory ILC dysfunction in the pathological state. Herein, we feature the group 3 innate lymphoid cells’ development, biological function, maintenance of gut homeostasis, mediation of IBD occurrence, and potential application to IBD therapy
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