Twenty-Third Symposium on Naval Hydrodynamics (2001) / Chapter Skim
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International Collaboration on Benchmark CFD Validation Data for Surface Combatant DTMB Model 5415
International Collaboration on Benchmark CFD Validation Data for Surface Combatant DTMB Model 5415
Pages 402-422
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From page 402... ...
tems, data-aquisition ad reduction procedures, ad once tamty assessment Results were discussed with dew ml to levels ad cases of data differences ad datadifference once tamties ad to estimate facility/model geomet y ad scale ettect biases For same size 5 7 m models, data differences were m ge off oscillate y, ad in may cases, larger in magmit de fha datadifference uncertainties, which mdicates maco mted for bias ad prey ision limits ad that Currff t individual faci it once tamty estimates a often too optimi tic Scale effects for the 3 m model ape only evident for resista e ad him tests at high Fr Faility/model geometry ad scale effect bias are estimated based on comparisons Unce tamty estimates including mch biases may provide better estimates, especially for use in CFD validation, which is the recommendation of She present tudy along with efforts towards improvement of Individual in titute uncfftamty e timates Use of standard models ad current ITTC effo ts m providing standard quality mamal procedures for towing lank tests ad uncertainty estimates will also be helpful m this regard INTRODUCTION Towing lank testing is mdergomg change from routine tests for global variables to detailed tests for local variables for model development ad · 23~3 Symposi m onNaval Hyd ody amics, 17-22 Septr 1 computational fluid dy mics (CFD) validation, as design methodology changes f om model testing ad theo y to simulation-based design Such detailed testing requires that towing tanks utili:D: advert d modem insh mentation with complete doc mentati m of test conditions, procedures, ad uncertainty assessment The requi ements for levels of uncertainties a even more stringent than those requi ed previously since Hey are a limiting factor m establishing She level of validation ad credibility of simulation technology Also, routine test data is more I kely utilized in house, whereas detailed test data is more Ikely utilized mtemationally, which additionally requi es use of standard procedures ad e ravishment of benchmark levels of data uncertainties D tailed testing offers new opport mities for towing tanks, as the amo mt ad complexity of testing is mcreased International collaborations a iterative from a resource perspective The benchmark database for CFD validati m for resista e ad propulsion is fanly extensive with current focus on modern hull forms a d detailed tests as repo ted by She Resi tan e Committee of the 22 International Towing Tak Co ference JTTC, 1999)
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From page 403... ...
Spch compa isoms betw en fapilities is apa ntly relaively p ommon m other fields such a arospae ad mechaica engip ering, which may be dp to mcrea cd complexity of roptme ship model testing dp to viscops ad f ee sp fae effects in compa ison to roptip testing m other fields The respits ae timely with pgad to the Godhenbp g 2000 Workshop on CFD for Ship Hydkody amics ad shopid be taken mto consideraion in reahing concipsions p ga dmg levels of CFD va ida ion The fopps hep in is on the overlaping tests; however, highlights a given of the overal test prog am S - tiom descr~be, respectively: the overlaping test desigm, compaison vaiales, ad conditions; failities, meap ffment systems, ad procedup s; p ertainty a sessments; CFD va ida ion/c om p lem enta y CFD; c om p a i s ons of re mit s; highlights of 6he overal test prog am; ad cop Ipsions OVERLAPPING TEST DESIGN, COAdPARISON VARIABLES, AND CONDITIONS The most typica towmgtak tests were selected for 6he overlapmg te ts, ie, p si ta e, si kage ad him, wa profile, we elevaions, ad nomma wake Eah mstitute follow d 6heir pspa procedp es; however, specia consideraion wa gi p to integ a ion of p ertainty a sessmffpt mto a I pha es of the experimenta process, CFD vaidaion, ad complementay CFD Compaison vaiales were defip d for tota CTJ1Se ad residpa y C~ resista e, smkage ~ ad trim ~, we profle_md elevaions (, ad nomina wake mea velocity V ad pp ssp e C~, a given by 6he followmg dma reduction equaions: CT = c~ + c~ (J + k)
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From page 404... ...
The IIPR tak is equipped with a elechic-motor opereed dkive ceriege the is cale dkiven by a 15-horsepower motor ad caale of speeds of 3 m/s Sidewall ad endwall beahes enale twelve-mincte intervals betw en cariege r ms Towing-tak weter is scpplied by 6he city of lowa City Model geometry. 5415 wes consh pted et 6he DTMB model workshop in 1980 f om a blak of lamineted wood ad a computerized n mericalcutting (CNC)
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From page 405... ...
Carriage speed. At each facility, carriage speed Uc is measured with encoder-based measurement systems and PC data acquisition.
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From page 406... ...
Wave profiles ~ are measured with different meiwcement systems ad normah:cd with model iengh L DTMB utili:oss a waterproof pencil ad hull-based g id sy tem for the wave profile tests Wave profiles a marked on the model as it is tow d 6 ouch be basin Vernier calipers a used to quatffy be wave profile heights referenced to be fullload water line NSEAN utilizes a photon Ethic ad digiti ing measurement system with a hull-based g id system for the wave profile te Is Data requisition is done by photographing be wave profile m sections (20% L) ad digiti ing She negatives with a highresolution scanter Wave heights are quantified t xstations on be model vifh CAD sof ware IIHR utilizes adhesive markers, tlex~l:le ruler, level tale, height gage, a d hull-based g id system for the wave profile te Is Data requisition is done by tixmg the adhesive markers t the top of be wave profile at each x-station The model is removed from the teak ad a flexible ruler is used to measure be wave profile dista e along the gi th of the model from be calm waterline The above two reps a repeated th ee times The model is Averted ad mo mted on a level tale ad be average wave height values a remarked along be gi th of the model from the calm w terline The height gage is used to measure be wave height z Far field wave elevations.
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From page 407... ...
, bo mdary layer pitot probe, pitot- tatic probe, five differential pressure transducers ad sigmal conditioners, 16-bit AD card, ad cariage PC for be nominal wake tests The fivehole probe is cabin red before acquisition of the nommal wake data Pitot tube calibr lion pressure coefficient ma ices a determined from the calibration measurements, performed on a calibration rig towed in calm water with no ship model present The calibration is expressed m coefficient form as: pitch ankle (Cal pitch) verms yaw ankles (C yaw)
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From page 408... ...
Uncertainty in ~ ad z et DTMB is somewhat le ge for F - O 10 but decreases sigmfficatly with mmeeding Fr cd the rage of the measurements inmeede, i e, be potentiometers opera e further from thei limiting resolution for higher Fr Bled limit contributions for both vaiahles me mainly effected by the t alter in She potentiometer calibrations ad decrease with mmeeding Fr Convert Iy, precision limit contractions mmeede wi6h mmeeding Fr which may Indicate elevated cc n we vibration for higher Fr ad or residual rank motions Uncertainty in a ad z et INSEAN is le ge for Fr=0 10 but dffreedes sigmfficatly to values compe able with DTMB wi6h inmeeding Fr Bled limits e e negligible for bodh ve iahles ad all Fr due to domma e of precision limits whose elevated values e e ariboted to redid tat rank motions between cc ridge r drS Uncertainty in a ad z et r HR is somewhat le ge for F - O 10 but decreases sigmfficatly wi6h inmeeding Fr cd per DTMB ad INSEAN Bled limit conh~botions for a e e high to mod r.de for Fr=0 10 ad F - O 28/0 41, respectively, with no Fr-depff dence Bled limit conh~botions for z e e high et F - O 10 ad decrease wi6h mcreedmg Fr cd 7
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From page 409... ...
probe positionmg m the te t region Uncertainty m be dista measurement D betw en be wave probes ad be FP of be model at t 0 acco mts for 6% of B . Unce tamty m the time lag betw en switch engagement ad data acquisition is negligible Precision limits a estimated with N=10 multiple tests ad conhibute sigmificatly to UP as per DTMB ad NSEAN Near field wave elevations.
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From page 410... ...
(A O in the HTR By, Bv, Bw, ad B D are mamly i fleeced by once tamties in She measurement of water head at She five-hole probe tip since She sin: of She tip is large with respect to the shear-flow g adients Bv ad Bw are also still affected sigmfficatly by uncertainty m the pitch ad yaw angles m She HTR Precision limits are estimated from N=10 multiple tests ad are ve y small in relation to She bias limits, which may be due to lack of free-surface turbulence/pitot-probe vibration CFD VALIDATION/COM PLEMENTARY CFD The conditions ad data locations ad densities (Tale 1) w re selected with consideration to use of data for CFD validation C vise Fr=0 28)
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From page 411... ...
All models were installed according to draft line, which is presumed the best method for CFD validation pur oses. However, it was noted by 22n~ ITTC uncertainty assessment example for resistance test that installation according to ballast weight reduces uncertainty in surface area by partially accounting for inaccuracy of design offsets.
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Former is considerably larger than for AB and latter is somewhat smaller. Clearly the differences for AC compared to AB for larger Fr are due to scale effects.
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Facility/model geometry biases are not evident for both sinkage and trim. Scale effect biases are not evident for sinkage and estimated as 12.2% for trim (Table 34.
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Results also show that scale effects for the 3 m model are insignificant. Average facility/model geometry and scale effect biases are estimated as 0.9% and not evident, respectively (Table 34.
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Trends are similar at y=0.082, except average data difference is only 0.6% and data-difference uncertainty is 2.8%. In this case uncertainty estimates include dependency on x.
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From page 416... ...
However, visual observation of wave patterns especially for higher Fr shows differences in wave breaking, i.e., wave breaking is considerably reduced for the 3 m model in comparison to the 5.7 m models presumably due to differences in Weber number and also some differences between wave breaking patterns for larger models presumably due to water quality differences between facilities A and B Average facility/model geometry and scale effect biases are estimated as 1.3% and not evident, respectively (Table 34.
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From page 417... ...
Results were discussed with regard to levels and causes of data differences and datadifference uncertainties and to estimate facility/model geometry and scale effect biases. For same size 5.7 m models, data differences were in general oscillatory, and in many cases, larger in magnitude than data-difference uncertainties, which indicates unaccounted for bias and precision limits and that current individual facility uncertainty estimates are often too optimistic.
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From page 418... ...
Longo, J and Stern, F., 1998, "Resistance, Sinkage and Trim, Wave Profile, and Nominal Wake and Uncertainty Assessment for DTMB Model 5512," Proc.
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Table 1: S mmary of ovsrlmpmgteF conditions for DT~, NSEAN, wmdllHR BXPBR3MBNT DTMB (A)
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Table 2: S mma~y of unce tamties i or DT=i, 1NSEAN, md IIER ovorl mping tests DTMB (A)
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From page 421... ...
The INSE N tank is relatively shallow compared to the model length Therefore, et high Proude Number some shallow water effect is expected AUTHOR'S REPLY The fomm factor is used only for date reduction es per ITTC, 1975 The k values are smell, i e, ~0 15 for each facility Shallow water effects are included in the blockage correction to carriage speed for each facility th ough the following equation Tcmurc's fommulc)
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From page 422... ...
varied somewhat in spite of the differences in towing height, the sirJcage Ed trim data was ve y uniform m magnitude for all models outside of the Fr r mge where scale effects are import mt, i e, Fr<0 33 11 ~let:3~e, it is not felt that towing point position was c signify mt factor in She metsured resi tance differences, Ether, She differences are I kely due to wave breaking The order of tests It each facility m temms of Fr was mdom DISCUSSION K I tmur3 Frof Nagasaki institute of Applied Science, Jcp m Thanks very much for your presenting She fundamental st dies on resist mce tests I would like to ask 3 questions 1) in page 9 of the text, you mentioned blockage effect, Ed I would like to ask you whether you conect the effect or not?
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