8,512 research outputs found
Design issues in the GCF Mark 4 development
Some of the major design problems facing the computer based Ground Communications Facility (GCF) Digital Communication System for the Mark 4 Network Consolidation Program are discussed. The solutions to each as implemented in the software of the GCF Operation Programs are proposed
Clustering and collision of inertial particles in random velocity fields
The influence of clustering on the collision rate of inertial particles in a
smooth random velocity field, mimicking the smaller scales of a turbulent flow,
is analyzed. For small values of the the ratio between the relaxation time of
the particle velocity and the characteristic time of the field, the effect of
clusters is to make more energetic collisions less likely. The result is
independent of the flow dimensionality and is due only to the origin of
collisions in the process of caustic formation.Comment: 4 pages, 3 figures, revtex
Some issues concerning Large-Eddy Simulation of inertial particle dispersion in turbulent bounded flows
The problem of an accurate Eulerian-Lagrangian modeling of inertial particle
dispersion in Large Eddy Simulation (LES) of turbulent wall-bounded flows is
addressed. We run Direct Numerical Simulation (DNS) for turbulent channel flow
at shear Reynolds numbers equal to 150 and 300 and corresponding a-priori and
a-posteriori LES on differently coarse grids. We then tracked swarms of
different inertia particles and we examined the influence of filtering and of
Sub-Grid Scale (SGS) modeling for the fluid phase on particle velocity and
concentration statistics. We also focused on how particle preferential
segregation is predicted by LES. Results show that even ``well-resolved'' LES
is unable to reproduce the physics as demonstrated by DNS, both for particle
accumulation at the wall and for particle preferential segregation. Inaccurate
prediction is observed for the entire range of particles considered in this
study, even when the particle response time is much larger than the flow
timescales not resolved in LES. Both a-priori and a-posteriori tests indicate
that recovering the level of fluid and particle velocity fluctuations is not
enough to have accurate prediction of near-wall accumulation and local
segregation. This may suggest that reintroducing the correct amount of
higher-order moments of the velocity fluctuations is also a key point for SGS
closure models for the particle equation. Another important issue is the
presence of possible flow Reynolds number effects on particle dispersion. Our
results show that, in small Reynolds number turbulence and in the case of heavy
particles, the shear fluid velocity is a suitable scaling parameter to quantify
these effects
Deploying a spreadsheet tool for early economic value assessment of medical device innovations with healthcare decision makers
Early stage evaluation of medical device innovations is important for healthcare decision-makers as much as for manufacturers, meaning that a wider application of a basic cost-effectiveness analysis is becoming necessary outside the usual expert base of health technology assessment specialists. Resulting from an academic-industry-healthcare professional collaboration, a spreadsheet tool is described that was designed to be accessible both to professionals in healthcare delivery organisations and to innovators in the healthcare technology industry who are non-experts in the field of health economics. The tool enables a basic cost-effectiveness analysis to be carried out, using a simplified decision-tree model to compare costs and patient benefit for a new device-related procedure with that of standard care employing an incumbent device or other alternative. Such a tool is useful to healthcare professionals because it enables them to rapidly elucidate the cost-effectiveness of heterogeneous innovations by means of the standard quality adjusted life year (QALY) measure of clinical outcome, which is intended to be broadly comparable across treatments. For the innovator or manufacturer it helps them focus on what is required for future stages of development, in order to fill gaps in the input data and so further strengthen their case from a health economics perspective. Results are presented of first experiences from deploying the tool on three medical device exemplars, in face-to-face meetings of the NHS National Innovation Centre (NIC) along with the innovator or clinical champion. The results show that mapping of device-related innovations to the tool is achievable in a short meeting between the NIC and the innovator using expected costs, outcomes data from the literature and estimates of ranges for unknown input data. Whilst the result of a simplified analysis is not expected to be definitive, the process of reasoning is found to be illuminating for the parties involved, enabling innovators to articulate the benefits of their innovations and for all parties to highlight gaps in data and evidence that will be required to take the innovation forward. The partnership model of the authors’ organisation supports the kind of cooperative design approach that is necessary to produce the kind of tool described.---------------------------7dd39101208fa
Content-Disposition: form-data; name="c14_creators_1_name_family"
Crave
Clustering and collisions of heavy particles in random smooth flows
Finite-size impurities suspended in incompressible flows distribute
inhomogeneously, leading to a drastic enhancement of collisions. A description
of the dynamics in the full position-velocity phase space is essential to
understand the underlying mechanisms, especially for polydisperse suspensions.
These issues are here studied for particles much heavier than the fluid by
means of a Lagrangian approach. It is shown that inertia enhances collision
rates through two effects: correlation among particle positions induced by the
carrier flow and uncorrelation between velocities due to their finite size. A
phenomenological model yields an estimate of collision rates for particle pairs
with different sizes. This approach is supported by numerical simulations in
random flows.Comment: 12 pages, 9 Figures (revTeX 4) final published versio
- …