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Since a few years, a new wind measurement instrument has been competing with standard cup
anemometers: the LiDAR. The performances of this instrument over complex terrain are still
a matter of debate and this is mainly due to the flow homogeneity assumption made by the
instrument. In this work, the error caused by this hypothesis was evaluated with the help
of OpenFOAM 1.7, MeteoDyn WT 4.0 and WAsP Engineering for a LiDAR deployed on a complex
site covered with dense forest. The assessment of the CFD model firstly revealed the
significant impact of both the location and nature of the inlet boundary condition.
Despite the presence of terrain complexity within a radius of 340 m around the remote
sensor, an averaged error of less than 3% was observed, suggesting that the LiDAR is only
affected by topographic variations in the immediate vicinity of the scanned volume.
An experimental investigation of the Marangoni convection around a single vapor bubble of
FC-72 on a downward-facing heated surface was reported. The boiling cell used for this
study was equipped with an optical measurement system which was dedicated to the Particle
Tracking Velocimetry (PTV) method. This method allowed us to obtain the velocity fields in
the liquid around the vapor bubble. From the velocity fields obtained, we verified the
presence of Marangoni convection rolls in the vicinity of the liquid-vapor interface.
Lastly, the influence of levels of subcooling on the velocity of convective rolls related
to the Marangoni effect was investigated.
For the unsteady simulation of compressible subsonic flows (Large Eddy Simulation or
Direct Numerical Simulation), the proper handling of the inlet boundary is a challenging
task. Indeed, inflow generation through imposition of the velocity may lead to a
non-physical reflection of the upstream acoustic waves. In the present contribution, a
method that allows both filtering of these waves and proper imposition of the required
variables is proposed. This method is based on identification of the roles of the temporal
rate of change of wave amplitudes at the inlet in the low Mach number regime. The
formulation obtained is tested numerically on unsteady one-dimensional flows at low Mach
number for which the unsteady inlet velocity signal is purely harmonic or harmonic with
the superimposition of synthetic turbulence.
This paper presents the analysis of the instabilities inception in a transonic
centrifugal compressor for different rotation speeds. The analysis was conducted from
experimental results obtained with unsteady pressure sensors implanted in the inducer,
vaneless diffuser and vaned diffuser. Beyond the stability limit the compressor enters
into a deep surge without any precursor, whatever the speed. The surge process is
initiated in the vaned diffuser by a massive boundary layer separation. For low speeds,
together with the surge which remains triggered in the diffuser, aerodynamic instabilities
are detected in the inducer. These instabilities can be understood as “tip clearance
rotating disturbances” because they are generated at the leading edge of the impeller main
blades and move along the tip clearance trajectory.
Water-lubricated bearings are expected to be widely used because of convenience, green,
safe and energy saving. The purpose of this study is to provide references for designing
hydrodynamic water-lubricated step thrust bearings. The numerical analysis is undertaken
under the condition of different pad dimensions, step heights, step positions, water film
thicknesses and rotational speeds of thrust rings based on computational fluid dynamics
(CFD). The results including pressure distribution, load carrying capacity, friction
torque and friction coefficient are gained and compared for optimizing geometry
parameters. A reference to determine water-lubricated step thrust bearing dimensions and a
formula to check the minimum water film thickness are proposed.
Today, to cope with the complexity of the global organization, the industrial company
needs to be more structured. New processes have to be developed due to more and more
ambitious quality requirements. A new problematic arises: what is needed to offer to all
customers a product that meets the quality requirements of a local market? The main
objective of this paper is to propose a quality requirements allocation method that
matches the market specifications and the customer satisfaction. This is in contrast with
the traditional allocation methods which are often time-consuming to implement or do not
focus on the customer satisfaction for the definition of the quality targets. The proposed
method is inspired from reliability allocation method and is formulated as a feasibility
problem. In this context the notion of optimality of the solution is not being sought, the
objective is “only” to find out a solution that satisfies the global target quality. This
allows determining some local quality targets in accordance with industrial data.
The objective of this article is to present the dimensional synthesis of serial and
parallel spherical wrists, an important step in the design process of medical robots. This
step is carried out to obtain optimal dimensions of tool-guidance medical robots. With
this goal, we have first studied the specifications of two robots with different medical
applications: one for tele-echography examination and one for minimally invasive surgery.
Then, we have established that the medical needs expressed by the doctors were very
different but the specifications in robotic terms have a lot of common points (kinematics,
workspace, bulkiness). For both applications studied, robots need a mobility of three
rotations around a fixed point (probe contact point on the patient’s skin or trocar
incision). So, a spherical wrist architecture is adapted to their needs. An important
constraint related to medical applications is that the robot must be compact in order to
not obstruct or collide with its environment (medical personnel or patient). We perform
dimensional synthesis allowing determination of dimensions of the mechanism for serial and
parallel spherical wrists, for a tele-echography robot, and a serial wrist for a minimally
invasive surgery robot. We use multi-criteria optimization methods minimizing a cost
function to obtain both good kinematic performance and compactness for the architecture.
The difficulty/challenge of this design process, depending of the studied applications, is
the choice of efficient criteria describing the performances and the constraints of the
robot. The design variables must faithfully represent the specifications of the robot so
that its performance can respond to the medical requirements. We show, here, the different
methods used for optimizing the chosen kinematic architecture for the particular medical
application. These studies lead to prototypes which are validated after medical
experiments. This process of dimensional synthesis will be applied to other medical
applications with different sets of specified constraints.
In this paper, a Levy-type solution based on the modified couple stress theory is
developed to study the buckling behaviors of micro-plates. Based on this theory, length
scale parameter is considered to capture the size effect of rectangular micro-plates.
Minimum potential energy and adjacent-equilibrium criteria are exploited to obtain the
stability equations and corresponding boundary conditions. Different boundary conditions
with two opposite edges simply supported and arbitrary boundary conditions along the other
edges are considered. To illustrate the new model, both uniaxial and biaxial loads are
applied and the critical buckling loads are defined for over a wide range of thickness,
different length scale parameters and various boundary conditions. To show the accuracy of
the formulations, present results are compared with available results in literature for
specific cases and a very good agreement is observed. Results reveal that the critical
buckling load increases as the length scale parameter increases especially when the
thickness of the micro-plates becomes in order of length scale parameter and this effect
is more significant for free boundary condition.
In this paper, we present techniques for fatigue damage evaluation using spectral methods
and a model taking into account confined elasto-plastic behavior. The model is associated
with a local fatigue approach, covering the whole endurance domain (low cycle and high
cycle fatigue). It uses Neuber’s method and is valid for limited plasticity. To validate
this modeling, we perform a correlation between spectral methods, modified spectral
methods and experimental tests. Results presented here are focused on the uniaxial loading