Twenty-Fourth Symposium on Naval Hydrodynamics (2003) / Chapter Skim
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Phase-Average PIV for Surface Combatant in Regular Head Waves
Phase-Average PIV for Surface Combatant in Regular Head Waves
Pages 898-915
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From page 898... ...
Animation of the nominal wake is achieved through Fourier-Series reconstruction of the velocity components. Comparison with forces and moment and wave elevation animations from previous study for same conditions indicates boundary layer contraction and expansion for local wave elevation increases and decreases, respectively.
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From page 899... ...
evaluate the nature of the head wave flowfield which will be used to excite the nominal wake of model 5512. Progressive wave results have demonstrated effectiveness of newly developed, phase-averaging techniques for unsteady PIV.
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From page 900... ...
The data-reduction equation for incident wave elevation is Its zing For unsteady PIV measurements, vector-map phase angle is defined Hi j =_ + D 271 _ ti 2~ where Gil is the 1St-hamonic phase angle of the jehincident wave, D is the distance between the servo wave gage and middle of the PIV measurement area, is the wavelength of the incident wave, ti is the time stamp of ith vector map, and Te is the encounter period. Steady post-processed variables include mean values, normal stresses, and shear stresses expressed below in equations (4146)
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From page 901... ...
Unsteady data is phase-locked to the incident wave elevation by connection of a servo wave probe to the PIV AD board. The probe monitors the incident wave either directly above the MA or from some distance D upstream of the MA.
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fe is then used in equation (3) to compute specific phase angle of all vector maps in each carriage run.
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f7-12) Compute phase angle for each vector map ~I: i=1,...,N,,,,; j=1,...,NC, equ (3J So vector maps _ _ on phase angle /)
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From page 904... ...
multiple test approach for precision errors. 2.7.1 Background Original development of UA procedures for steady PIV measurements were undertaken to commission the IIHR towed PIV system and document the quality of nominal wake data (Gui et al.
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UX=4B2+PX (30) Uncertainties in Tables 1, 2, and 3 represent average values from 62 grid locations at the nominal wake plane, i.e., x=0.935 (i=6, j=1-62)
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From page 906... ...
The results are organized with initial discussions of the 5512 steady flow including comparisons previous and current PIV results. Then, the incident wave elevation and flowfield measurements for Ak=0.025, ~4.572 m are discussed to evaluate the nature of the inflow for unsteady PIV.
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7. Summary of current steady mean and turbulent PIV measurements is shown in Fig.
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From page 908... ...
3.2 Incident wave elevation and flowfield For the unsteady tests, time histories of the incident head wave Czar are fundamentally important for establishing the phase angle of each PIV vector map.
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From page 909... ...
3.4 Unsteady flow 3.4.1 oth harmonic versus steady Differences between oth harmonic and steady mean and turbulence variables are facilitated through data acquisition of steady and unsteady datasets at the same locations. Percent-difference contours and datadifference vectors are shown in Fig.
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From page 910... ...
The former is centered on the location of peak unsteady turbulent kinetic energy and together with the largest region of Us bracket a modest area where unsteady effects are largely absent in Ul. In the outer flow, Ul decreases with increasing depth and is constant for all y at deepest elevations as per 2D progressive wave theory prediction.
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From page 911... ...
Although only four instances are shown, relative changes of contours reveal time-varying behavior of the boundary layer. At t/Te=O, incident wave trough is ~J4 upstream of the nominal wake plane, i.e., the local free surface elevation at x=0.935 is decreasing with time and the boundary layer is undergoing expansion.
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From page 912... ...
have been measured and conform closely with 2D progressive wave theory. Current steady flow mean and turbulence results are within the measurement uncertainties of previous steady PIV measurements which validates current data acquisition and data-reduction procedures where the latter were developed specially for the current steady and unsteady tests.
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From page 913... ...
Longo, J., Rhee, S.-H., Kuhl, D., Metcalf, B., Rose, R., and Stern, F., "IIHR Towing-Tank Wavemaker," Proceedings of the 25th ATTC, Iowa City, Iowa, 1999. Longo, J., Shao, J., Irvine, M., Gui, L., and Stem, F., "Phase-Averaged Towed PIV Measurements for Regular Head Waves in a Model Ship Towing Tank" Proceedings PIV and Modeling Water Wave Phenomena, Cambridge, UK, 2002, (to appear)
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From page 914... ...
Combatant," Proceedings of the 23 ONR Em on Naval Hydrodynamics. National Academy Press, 2001, pp.
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From page 915... ...
AUTHORS' REPLY Thank you for your question. The phase of the incident wave at the PIV measuring plane is computed with equation (3~.
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