Twenty-Third Symposium on Naval Hydrodynamics (2001) / Chapter Skim
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Forces, Moment and Wave Pattern for Naval Combatant in Regular Head Waves
Forces, Moment and Wave Pattern for Naval Combatant in Regular Head Waves
Pages 46-65
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From page 46... ...
, The University of Iowa Iowa City, A 52242, USA ABSTRACT A model-scale naval surface combatant, DTMB 5512, is studied experimentally in steady forward speed ad regular head waves with the Iowa institute of HydLalic Research BOHR) towing tank facilities Un teady resista e, heave force, pitch moment ad free-surfae elevations ape investigated with different measurement syst ms for a fanly wide rage of te t conditions Test data is procured for validation of RANS CFD codes ad for mderstading the physics of msteady ship hydkody amics Uncertainty assessments are completed following She A AA Standard The remits ad discussions for She forces ad moment cover the time mea values, added resista e ad linear ad non-linear responses Results of free surfa elevation te ts include reconstructed msteady wave patterns, diffraction wave patterns, ad free surface turbulence dishibutions 1.
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From page 47... ...
In addition, a detailed mapping of unsteady free-surface elevations is conducted for a selected test condition. In comparison to previous works, the present study provides much more detailed data with rigorous uncertainty assessment for CFD validation and systematic analyses of the flow physics in ship hydrodynamics covering non-linear responses of forces and moment and distributions of free surface turbulence.
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From page 48... ...
neurtield elevations) Thus, a phase shift is necessary to determine the reference phase Unsteady time histories are reconvey red with FS When the phase of the reference wave, i e the incident (5)
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From page 49... ...
the added resistance CT,a`, and the unsteady perturbation response of unsteady free-surface elevation, i.e. the diffraction wave (D, and they are defined as CT ad CT CT'S~ 2 ~ (16)
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From page 50... ...
cuts, paced at fly O 01 between the maxim m beam of The model ad the sidewall damper The data acquisition is triggered with photoelectric switches 9 seconds prior to the model FP passmg The wave probes ad ended when the measurement region is completely scatted The total time interval for data acquisition is 13 3 seconds, ad 2700 samples are recorded in every carriage r m 15-25 carriage r ms are pe formed at each constat-y cut to ensure a satisfactory di tr~bution of incident wave phases at The bedimming of the raw time histories As a example, one of The raw time histories (z, y, t l I taken at y 0 082 is show in Fig 4 Note That The incident wave is record d in The initial 9 seconds, ad this i fommation is used to detemmine the initial phase (Y) In the model coordinate system (x, y, /)
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From page 51... ...
In the post-processing procedure, the reference phase is determined according to the time history of the incident wave, and the FS harmonic amplitudes and phases are computed for unsteady free-surface elevations. The phase of the incident wave at probe 2 is determined with the first harmonic phase of the sampled wave elevation A,.
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From page 52... ...
of the bias g adient, which can be calculated with the data reduction equation ad elementary bias limits The bias limit of the perch FS harmonic amplitude is determined as 2 ~ BE = , | Bent = 2Bx According to Eq (43) the bias limits of the FS harmonic phases equal zero, i e P =0 The bias limits of She adjusted phases 3_s)
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From page 53... ...
Note that the incident wave elevation in the figure represents a nearly perfect first harmonic signal during She initial 8 seconds of She time hi tory but is somewhat distorted m the foal 2 seconds due to the closing distance between wave probe ad ship model The :osroth-harmonic amplitude is less than 1% of the fi st-hamonic amplitude ad the uncertdinty in wave f equency f ad wave amplitude A is 0 7% ad 2 65%, respectively, which is based on multiple tests N=ll) ad estimates of the bias limits Also based on multiple tests, She uncertamty of She enco mter frequency f is determined with time histories of CM Fig 8d 1 as 0 4% for She media test case which ensures acuray m the time domain of the measurements Note that f is determined with low r uncertamty th m f, because CM includes more wave periods than Zb i e f f The once tointy of f, A, ad f for the wazeeievations tests is expected to be at le ff as good as for the media test case 5.2.
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From page 54... ...
is larger than the steady resistance coefficient CT S~ Uncertainty assessment results for the FSreconstructed time histories are plotted in Fig. 10 as uncertainty bands.
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From page 55... ...
5.3. Linear response for forces and moment Sit e the regmlar head waves get rated by the IIBR wave maker a typical fi st-order harmonic waves, She et otmtet d waves by She ship hi 11 with a constant forward speed are also fi st-order harmonics When likening the ship hi 11 md the ff otmter wave ystem to a dy comic (oscillating)
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From page 56... ...
14: Zffoth md first FS harmonic amplit de md the first FS harmonic phase for CM The zerffh md fi st FS harmonics of the pitch moment coefhcient are plotted m Fig 14 Only slight differences are observed for CMO betw en the teady md msteady cases at low Fr Fig 14a) CM O mcreases nonlinearly with increasmg Fr md slightly wish increasmg Ak at low Fr Fig 14a)
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From page 57... ...
Nomlinear response for forces and moment In above discussions She fi st-order harmonic responses m She present ship hull ad wave y rem a considered as linear responses That implies that all the sub- ad super harmonics in She test results a referred to non-linear responses According to She analysis in subsection 5 2, the msteady responses of CT, Ce are CM are mostly Imear m She media test case because She harmonics a considered to be noises ad She super harmonics can be neglected ~ consideration of other test cases, the time histories ad the corresponding FT results of CM are given in Fig 16 12 15/00
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From page 58... ...
verses Fr md AL Detailed inve tigation of msteady responses for the sho t-wave case 6 ouch malysis of the Ig, 2~3 md 3-d FS harmonic amplitudes for C md Cb verses Fr md Ak is provided in Fig 17 The FS harmonic amplitudes for n=l, 2, 3 generally increase with increasing Ak, md they are roughly Imear functions of Ak except for cases at F - O 41 which mpear to be par:~olic The super 13 harmonics mpear to have signitlcmt magnitudes for F - O 34 md 0 41 The tendencies in the FS harmonics noted ibm H are similar for CM but not show here The conclusions from Figs 16 md 17 point to non-linear msteady responses m The forces md moment coefficients but mly for combinations of sho t ~ md mid-high md high Fr Further inve tigation of The super harmonics are shown in Fig 18, m which The dependencies of the FS harmonic amplit des on Fr for Ak=0 I md \=1 524 are given For C, Cb md CM, the first harmonic amplitudes decrease with increasing Fr, md the thi d harmonic amplit de. are relatively ve y small Interestmgly, for all th ee vari:3} lies The second harmonic amplitude has a maxim m near Fr=0 34 eU,,[IO1 5 :~[101 \ ~ [rl 4 5 \ ~ [r \~_.,2 : '\k j e,,,[101 zo; \ ~ trl 18f Wri 12 5 \ 10 ~ ~ B~ 05 ~ 0~zoz5 o~ 035 O .
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From page 59... ...
for the unsteady free-surface elevation 5.5. Free surface elevations The free-surface elevation data provided for CFD validation includes the FS-reconstructed unsteady freesurface elevations and uncertainty assessment results.
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From page 60... ...
The maximal amplitude of the diffraction wave (0.004) is about 40% of that of the unsteady free surface elevations.
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From page 61... ...
SUMMARY AND CONCLUSIONS Present mvestigations are aimed Itt procurmg validation data for RATS CFD codes ad explication of flow physics regading DTMB model 5512 in 16 12 15/00
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From page 62... ...
The maximal amplitude of the diffraction 17 wave is about 40% of that of the unsteady free surface elevation. The phase distribution indicates that the diffraction waves originate from the forebody and stern regions of the model.
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From page 63... ...
, Stern Flow Measurements for 6he Taker 'Ry ko-Maru' m Model Scale, Intemmediate Scale, ad Full Scale Ships P'oeeedmgs of CFD Workshop Tokyo 1994, Vol 1, pp 341-349 RheeSH, SteruF (1998) , Unsteady RANS Method for Surfae Ship Bo mdary Layer ad W ke ad Wave Field 3ff OSA A C llogulum on Adwmeed CFD Applicahons to Ship Flow md Hull Form Design, May 25-27, 1998, OSAKA, Jaa Roth GI, MaseerdkDT, KatzJ (1999)
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From page 64... ...
36, No 4, pp 360377 Van SH, Kim WJ, Yim GT, Kim DH, Lee CJ (1998) , Experimental Irme ligation of She Flow Charateri tics Aro Ed Practical Hall Forms Proceedings 3~ Osaka Colloquium on Adwmced CFD Applicahons to Ship Flow md Hull Fo m design, OsAca, Java WdsonR, Patemon E, SternF (1998)
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From page 65... ...
AUTHOR'S REPLY The diffraction waves are 67% of the incident wave height, i.e., (0.004/0.006)
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