Trans RINA, Vol 156, Part B2, Intl J Small Craft Tech, Jul-Dec 2014
The model is manufactured as a “rigid aerodynamic model”, that is a static model that reproduces the geometry of the full-scale structure (aerodynamic surfaces and details). Figure 4 shows an example of a mega-yacht scale model.
modules. The calibration of the RUAG 192-6L balance is released by RUAG Aerospace defining error classes for each possible load case combinations up to simultaneously given loads
directions [17]. Table 3 reports the Maximum absolute error and the absolute Standard Deviation as percentage to the design loads.
The tests have been done with applied loads which are very low compared to the design ones. Moreover, during the tests, only static loads have been applied to the balance so that no dynamic effects can influence the errors. Moreover the transducers and
amplifiers uncertainties could be
Figure 4: Mega-yacht scale model. 3. YACHT AERODYNAMICS ASSESSMENT 3.1 FORCE MEASUREMENT
The measurement of the overall wind loads on the hull and yacht
superstructures is achieved using a six
component force balance, which is generally placed inside the hull. The model is usually manufactured using an internal structural frame which is rigidly connected to the dynamometer.
The dynamometric balance used has seven strain gauged channels which, thanks to a suitable calibration matrix, permit highly accurate measurement of the three forces (vertical, longitudinal and lateral) and the three moments around the three principal axes.
The yacht aerodynamic forces are generally measured at different angles of attack from 0° to 180° with a step of 15 degrees:
results are presented as function of the
exposure angle (α) in the wind coordinates system, in terms of drag coefficient, side (lift) force coefficient and aerodynamic moment coefficients.
Table 3: Max absolute errors and Std dev absolute as % of the design loads
Force component
Max error absolute in % of design load
Fx -0.39 Fy
Mx My Mz
-0.65 0.37
-0.17 0.15
Std. dev. absolute in % of design load
0.093 0.10
0.049 0.045 0.039
The balance is a RUAG 192-6L and the conditioning and amplifying system is a HBM MGC PLUS with MC55
Figure 5: Irwin probes map on the Sun deck and experimental set-up. B-74 © 2014: The Royal Institution of Naval Architects
considered negligible. 3.2 SPEED-UP MEASUREMENT Comfort evaluation
according to 3 different
on the various yacht decks
and
recreational areas are performed by means of wind speed measurements carried out in different positions according to yard and designer specifications (typically on yacht terraces and yacht decks) considering different wind exposures.
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