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Keyword : analyses
Results 1 - 5 of 44
A Comparison of a RANS Based VPP to on the Water Sailing Performance
This paper compares performance predictions from a
Reynolds Averaged Navier Stokes (RANS) based Velocity
Prediction Program (VPP) to on the water testing of a J70.
The J70 has been outfitted with a system to determine sail
flying shapes, apparent wind conditions and performance
data. The on the water testing is conducted in both racing
and controlled sailing conditions. Data taken during racing
conditions is analyzed to determine optimal performance
envelopes while data taken in controlled conditions is used
to match exact sailing and VPP states. The data acquisition
system combines a number of standard marine sensors
including a sonic anemometer, a GPS, a digital compass, an
accelerometer and a gyroscope with custom sensors that
measure rudder and boom angles as well as a custom sail
shape acquisition system. The RANS based VPP developed
by Doyle CFD has three main components; an aerodynamic
force model, a hydrodynamic force model and an algorithm
to balance the forces. The force balance routine uses four
degrees of freedom; boat speed, yaw, heel and rudder angle
to balance the aerodynamic and hydrodynamic forces for a
given true wind speed and angle. The force models are
derived from RANS CFD data calculated using
OpenFOAM. The aerodynamic forces are calculated using
steady state RANS as a function of apparent wind angle,
apparent wind speed and sail flying shape. The VPP force
model is derived by fitting response surfaces to this data.
The aerodynamic CFD is run with sail flying shapes
recorded from on the water testing. Using accurate flying
shapes is critical for picking out slight aerodynamic
differences in sail and rig setup. The hydrodynamic CFD
data points are calculated using RANS Volume of Fluid
CFD (VOF) as a function of boat speed, rudder angle, yaw
angle, heel angle and displacement. Response surfaces are
generated from a 128 data point array of RANS VOF
simulations.
In small sailboats, the bodyweight of the sailor is proportionately
large enough to induce significant unsteady dynamics
of the boat and sail. Sailors use a variety of techniques
to create sail dynamics which can provide an increment
in driving force, increasing the boatspeed. In this
study, we experimentally investigate the unsteady aerodynamics
associated with one such technique, called “sail
flicking”. We employ a two-part approach...
Modal Analysis of Pressures on a Full-Scale Spinnaker
While sailing offwind, the trimmer typically adjusts the
downwind sail "on the verge of luffing", letting occasionally
the luff of the sail flapping. Due to the unsteadiness
of the spinnaker itself, maintaining the luff on the verge of
luffing needs continual adjustments. The propulsive force
generated by the offwind sail depends on this trimming and
is highly fluctuating. During a flapping sequence, the aerodynamic
load can fluctuate by 50% of the average load.
On a J/80 class yacht, we simultaneously measured timeresolved
pressures on the spinnaker, aerodynamic loads,
boat and wind data. Significant spatio-temporal patterns
are detected in the pressure distribution. In this paper we
present averages and main fluctuations of pressure distributions
and of load coefficients for different apparent wind angles
as well as a refined analysis of pressure fluctuations, using
the Proper Orthogonal Decomposition (POD) method.
POD shows that pressure fluctuations due to luffing of the
spinnaker can be well represented by only one proper mode
related to a unique spatial pressure pattern and a dynamic
behavior evolving with the Apparent Wind Angles. The
time evolution of this proper mode is highly correlated with
load fluctuations.
Moreover, POD can be employed to filter the measured pressures
more efficiently than basic filters. The reconstruction
using the first few modes allows to restrict to the most energetic
part of the signal and remove insignificant variations
and noises. This might be helpful for comparison with other
measurements and numerical simulations.
Sailing is a sport and activity that takes a long time both
to learn and to master, as much of its competence-based
knowledge is acquired through experience. Experiencebased
learning is very important, time-intensive, and the
factors for success are often tacit and hidden. Should these
success factors become explicit and salient, learning would
occur faster and produce obvious competitive advantages.
This research was conducted by embedding on-going
research results into two competitive sailing teams racing
in different classes, one offshore keelboat racing with a
crew of eight, and a one-design Star-class racing yacht with
a crew of two. The data collection consisted of
observations, interviews, and video recordings. The results
were also verified with the crews to catch biases in the
analysis process. A jibe, a specific but common maneuver
was analyzed from the perspective of Common Ground
within Joint Activity.
Maneuvering a competitive offshore sail racer or a
previously Olympic Star-class yacht are tasks that fulfill
the requirements for Joint Activity. A high level of
Common Ground is required for the effective coordination
needed in order to perform at a high level and maintain the
safety of the crew and equipment.
Breakdowns in the coordination of maneuvers were
observed, although they must be recorded on video for
higher analysis reliability. To achieve greater validity,
more and different maneuvers should be considered within
the analysis.
By better understanding the factors for success, sail
racing teams can more quickly gain competence and thus
competitive advantages.
The research analyzes the teamwork found in sailing
from the perspective of Joint Activity and Common
Ground and provides insight into how to achieve
performance improvements more efficiently.
Uncertainties in the Wind-Heel Analysis of Traditional Sailing Vessels: The Challenges it Presents for Forensic Analysis of Sailing Vessel Incidents
There are many uncertainties in the interpretation of
full-scale sailing vessel data taken under dynamic
conditions, and even more uncertainties when
forensic analysis is attempted based only on
survivor’s recollections. Frequently, the analysis is
based on static equilibrium assumptions, sometimes
modified to steady-state motions of the wind and
heeling response of the vessel. Dynamic conditions
are generally non-deterministic and statistical
methods must be used. Even more complicated is the
non-stationary random process nature of most
accidents.
In the wind-heel research carried out on Pride II, it
has been shown that wave action frequently adds
uncertainty to the correct attribution of contributions
to establishing the cause of the resulting heeling
action. The best data are found in steady 10 to 20
knot wind strengths in minimum waves found in the
lee of a shoreline. This criteria can be interpreted as
minimizing the uncertainties in characterizing the
wind-heel performance of a given sail combination at
normal angles of heel...