Prof. Frederick SternUniversity of Iowa, IIHR, USA

Maneuvering Committee

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Complementary CFD, EFD, and UA philosophy includes:◦ CFDSHIP-IOWA simulations◦ Towing tank and flume experiments◦ Uncertainty analysis (UA)

Leaders in using standard UA techniques for ship hydro data.◦ Verification and validation

CFD is used to guide EFD and EFD is used for CFD validation and mathematic model development.

CFD is validated and fills in sparse EFD data for complete documentation and diagnostics of the flow.

World’s first implementation of towed, stereo PIV flow map system for towing tank application is the latest effort towards the philosophy on EFD side.

IIHR ShipIIHR Ship--hydrodynamicshydrodynamics

A brief history of IIHR towing tank PIV works◦ 1st Generation: 2D-PIV (1995 – 2004)

◦ Nominal wake field measurement◦ Forward speed diffraction problem◦ Roll decay motions

◦ 2nd Generation: Stereo 3D-PIV (2005 – today and beyond)◦ PMM maneuvering◦ Wave breaking and instability problem◦ Solid/Free-surface juncture boundary layer and wake

◦ 3rd Generation: Tomographic PIV† (later 2009)◦ Free running model tests in IIHR wave basin‡

† Transition to 3 or 4 camera 3D-PIV still being decided; ‡ In the design phase.

2D-PIV System (DANTEC)

Stereo 3D-PIV System (LaVision)

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1. Test Design1) Test Conditions2) PMM3) Stereo PIV System4) PIV Image Acquisition and Vector Correlations

2. Uncertainty Analysis

3. Results1) PIV Measured Flow Field2) Comparisons with CFD3) SIMMAN 2008

4. Concluding RemarksHull form for PIV tests: DTMB 5512(5415)

Unsteady PIV for PMM ManeuveringUnsteady PIV for PMM Maneuvering

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Overall PMM test programOverall PMM test program

PIV conditions◦ Two (2) types of PMM

Pure sway test Pure yaw test

◦ One (1) speed Fr = 0.280

◦ Model degree of freedom Fixed at the dynamic sinkage and

trim condition†

marked in red : PIV cases

† sinkage = 1.92110-3LPP; trim = -0.136 (bow down)

The force/moment measurements and UA are part of a collaboration with FORCE Technology (DMI), INSEAN, and the 24th –25th ITTC Maneuvering Committee.

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PMMPMM Design and construction is a collaborative effort by

◦ Sanshin Seisakusho Ltd. (mechanical system)◦ Mori Engineering Ltd. (electrical system) ◦ A 4-m strongback mounted to support equipment and a

point of attachment for a ship model. ◦ A two-dimensional, automated traverse is suspended

from the strongback to hold the PIV system.

Perspective view Top view Front view Side view

Parameter (unit) Specification

Mechanical system Scotch-yoke type

Servo motor (kW) 11

Max. PMM frequency (Hz) 0.25

Max. sway amplitude (mm) 500

Max. yaw amplitude () 30

Perspective view from underneath

Krypton camera

Strongback

3D-PIV

Model 5512

PMM carriage

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Stereo PIV SystemStereo PIV System A LaVision Inc. custom-designed and built system.

Geometrical Layout

◦ The laser and lightsheet optics are arranged to deliver a vertical lightsheet in the (y,z) crossplane.

◦ The cameras are arranged asymmetrically in submerged enclosures downstream of the lightsheet to minimize wave and flowfield effects of the enclosures at the measurement area.

Item Parameter (unit) Specification

Laser TypeEnergy (mJ)

Nd:YAG (dual head)120

Light sheet Lens config.Sheet thickness (mm)

2 spherial + 1 cylindrical1.0 – 5.0 (adjustable)

CCD camera Resolution (pixels)Max. rate (fps)

1600120030

Particle Average dia. (m)Specific gravity

141.7

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PIV Image AcquisitionPIV Image Acquisition PIV image acquisition

Pure sway: 8 phases per each PMM cycle. Pure yaw: 32 phases per each PMM cycle.

x/LPP = 0.135 x/LPP = 0.335

x/LPP = 0.535 x/LPP = 0.735

x/LPP = 0.935 x/LPP = 1.035

Pure yaw test

Image acquisition is completed at several overlapping zones at each x-station. Pure sway: x/LPP = 0.135, 0.235, 0.735, 0.935 Pure yaw: x/LPP = 0.135, 0.335, 0.535, 0.735, 0.935, 1.035

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Vector CrossVector Cross--correlationcorrelation PIV recordings are processed

with LaVision DaVis v7.2 software. Multi pass cross-correlations

(128128 6464 3232 pixels interrogation windows).

50% overlap in the horizontal and vertical directions on all correlation passes.

Standard I1I2 correlation via FFT.

High accuracy Whittaker reconstruction.

Vectors are range filtered, and then a median filter follows, removing vectors if their magnitude is greater than two times the rms value of their neighboring vectors.

Spurious vectors are not replaced with interpolated values, and blank spots in the measurement area are not filled.

Pure yaw test at x/LPP = 0.935 zone #2

PIV images from camera #1, #2 and frames A, B produce correlatedinstantaneous vector fields at 32 phases

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Statistical convergenceStatistical convergence Convergence is evaluated with phase-averaged variable residuals.

Ek is a running mean residual computed from k and k-1 recordings.

A two-order drop in rms Ek over the measurement area is desired and ensures that the variable is not changing by more than 1% of its dynamic range as more PIV recordings are added.

A value of 1% is assumed to be within the uncertainty range of any mean or turbulent flow variable.

To minimally achieve statistical convergence of phase-averaged mean variables, the PIV image number is determined at about 250 images per zone; this corresponds to 100 carriage runs per zone.

k: Number of images

<E

k> rm

s101 102 103

10-7

10-6

10-5

10-4

10-3

10-2

10-1

UVWuuvvwwuvuwvw

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Uncertainty AnalysisUncertainty Analysis UA procedure follows ITTC Procedures 7.5-02-01-01 Rev 00 and 7.5-02-01-02 Rev 00 which are based on

AIAA (1995) standards and guidelines which in turn are based on the work of Coleman and Steele (1999). The overall approach is based on large sample size/normal distribution ninety-five percent level of confidence

assumptions with estimates of systematic bias (B) and random precision limits (P) and their root-sum-square (RSS) combination to ascertain total uncertainty (U).

Bias limits are evaluated by performing uniform flow and PMM without model tests to isolate B’s rather than by applying error propagation equations to DRE’s where the mapping functions are typically not easily defined by the end users; B’s are also evaluated for x, y, z spatial errors and temporal (t) errors.

Precision limits are evaluated with repeat tests but with limited number, three (M = 3) times, M >3 is cost-prohibitive.

Ongoing UA includes calculation of B’s, P’s, U’s Future UA will follow latest ASME (2005) standards and guidelines

Phase

Uid

eal,

U

Vid

eal,

V,W

0 50 100 150 200 250 3000.92

0.94

0.96

0.98

1

1.02

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Phase

Uid

eal,

U

Vid

eal,

V,W

0 50 100 150 200 250 3000.92

0.94

0.96

0.98

1

1.02

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Pure sway Pure yaw

PMM without model test

Test U (%UC) V (%UC) W (%UC)

Uniform flow

1 2 1

Pure sway (no model)

1 2 0

Pure yaw(no model)

1 2 1

Preliminary results

: difference between the expected and measured values

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Test Results Test Results (Pure yaw test)(Pure yaw test) Phase-averaged axial velocity, turbulent kinetic energy, and axial vorticity contours are shown Flowfield results indicate maneuvering-induced vortices and their interactions with the turbulent

boundary layer. Data is needed at additional x-stations in the boundary layer and wake and on the free surface in

order to connect the flow structures and enable conclusive statements about the flow physics. Complementary CFD simulation results are also needed for comparisons with the EFD results to

aid in the analysis of the data.

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Comparisons with CFDComparisons with CFD†† (Pure yaw test)(Pure yaw test)

† SIMMAN, 2008

Axial velocity contours

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Phase-averaged axial velocity field is compared with CFD simulation result.

CFDSHIP-IOWA Ver.4: RANS Chimera/Overset grid 5.47M grid points SST k-/k- turbulence model Level set free surface treatment Finite difference method

CFD simulation results show good agreement with phase-averaged PIV measurements.

CFD tends to over-predict axial velocity magnitude at the sonar dome vortex core particularly at down stream stations.

Turbulent kinetic energy contours

Comparisons with CFDComparisons with CFD (Pure yaw test)(Pure yaw test)

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Phase-averaged turbulent kinetic energy field is compared with CFD simulation result.

CFD simulation shows good overall agreement in turbulent structures with EFD data.

However, CFD tends to under-predict flow turbulence particularly at down stream regions.

RANS DESPIV

Comparisons with CFDComparisons with CFD†† (Pure yaw test)(Pure yaw test)

† CFD: Iso-2nd invariant surface plotsPIV: Phase-averaged axial vorticity contours

14Vortex structure (static drift = 10)

Global structures are similar between URANS and DES.

Local structures are different: DES resolves longer SD, helical instability of SD and FK, K-H vortices at leeward side bow, and transom shedding.

CFD under-predicts axial vorticity strength at the vortex core region.

Comparisons with CFD Comparisons with CFD (Forces/moment )(Forces/moment )

Static drift test:

Pure sway test:(max = 10)

Pure yaw test:(r’0 = 0.3)

|E| (%D) X’ Y’ N’

Static drift1) 3.8 10.6 0.2

Pure sway2) 403 3.4 3.8

Pure yaw2) 60.1 12.5 2.0

1) at = 102) dominant harmonic amplitude

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For static drift, discrepancy between CFD and EFD becomes larger for larger drift angles.

For dynamic tests, CFD and EFD show apparent differences in force/moment amplitude and phase for X’, whereas those show good agreements for Y’and N’

SIMMAN2008SIMMAN2008(Workshop on Verification and Validation of Ship Maneuvering Sim(Workshop on Verification and Validation of Ship Maneuvering Simulation Methods)ulation Methods)

Test Hull Forms: KVLCC, KCS, 5415 Approach: Systems/CFD Based Methods Test cases for 5415(bare hull) using CFD Based method:

◦ 3a-1 static drift test ( = 0 and 10)◦ 3a-2 pure sway test (at the PIV conditions)◦ 3a-3 pure yaw test (at the PIV conditions)

Participants :◦ BEC-ECN (France) †

◦ ECN/CNRS (FRANCE) †

◦ IIHR (USA) †

◦ NSWCCD (USA)◦ UMNSWCCD (USA)

- : not specified

Simulation specifications

† simulated the PIV cases

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Test case 3a-2: pure sway test (x/LPP = 0.935) All three CFD simulations show good agreements with the PIV data in terms of

overall flow pattern and axial velocity magnitude

Axial velocity U contours and cross flow vectors V, W

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Transverse velocity V

Test case 3a-2: pure sway test (x/LPP = 0.935) For transverse velocity component, the prediction results of CFDSHIP-IOWA show better prediction

results than other CFD codes.

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Vertical velocity W

Test case 3a-2: pure sway test (x/LPP = 0.935) For vertical velocity component, both ISIS and CFDSHIP-IOWA prediction results show good agreements

with PIV data in general.

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Mean velocity

Test case 3a-3: pure yaw test (x/LPP = 0.335) Only CFDSHIP-IOWA submitted simulation results.

The overall prediction results show excellent agreements with the PIV data seemingly qualitatively and quantitatively.

Turbulent kinetic energy Axial vorticity

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Mean velocity

Test case 3a-3: pure yaw test (x/LPP = 0.935) However, CFDSHIP-IOWA simulations at the downstream region tends to under-predict flow turbulence

and axial vorticity magnitude particularly at the sonar dome vortex core region.

Turbulent kinetic energy Axial vorticity

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SummarySummary Towed stereo 3D-PIV successfully implemented at the IIHR towing tank for measurements of unsteady

dynamic PMM maneuvering flowfields.

The system consists of a collaborative Sanshin & Mori PMM system, LaVision Inc. custom-designed and built stereo PIV system, and LaVision DaVis v7.2 software.

Measured flow data were phase-averaged followed by mean and turbulent flow variable computation. Statistical convergence was monitored with variable running mean residuals, and the optimal number of PIV images determined at about 250 to meet both convergence and time constraints.

UA is ongoing; preliminary results from uniform and PMM without model test results show about 1%, 2%, 1% bias uncertainty in phase-averaged U, V, W velocity components, respectively…spatial (x, y, z) and temporal errors to be computed as well as precision uncertainty and total uncertainty.

Comparisons with CFD show generally good agreement of global flow structures, whereas CFD under-predicts the turbulence kinetic energy and axial vorticity strength especially at down stream regions. Additionally, comparisons of forces and moment data also show good agreement between EFD and CFD results except for the longitudinal force component X’ data.

The PIV results were used as benchmark validation data for SIMMAN 2008 and compared with several CFD simulation data.

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Future direction of PIV at IIHRFuture direction of PIV at IIHR Towing tank PIV for validation of two-phase CFD

Captive model 5613

Stereo PIV in air

Sanshin/Mori wind generator

Maneuvering and seakeeping tests in a wave basin Free, self-propelled model 5613

Stereo PIV shadows free-running model

Sanshin/Mori wavemakers, bridge crane, and tracking system

Tomographic PIV, i.e., three or four underwater camera and thick lightsheet application to… Towing tank testing

Flume for wave breaking tests

Wave basin free model maneuvering and seakeeping testing

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Concept drawings of IIHR wave basinshow basin, wavemakers, bridge crane, and beach

(top) and stereo PIV system shadowing model 5613 from an automated bridge crane during data

acquisition (bottom)

AcknowledgementsAcknowledgements This research was sponsored by the Office of Naval Research under Grant N00014-01-1-0073 under

the administration of Dr. Patrick Purtell whose support is greatly appreciated.

Special thanks are extended to Prof. Yasuyuki Toda, Sanshin Seisakusho Ltd., and Mori Engineering Ltd. (IIHR PMM system)

Dr. Steve Anderson, LaVision Inc. (IIHR stereo 3D-PIV system)

U of I undergraduates Matt Marquardt, Mike Elgin, Peter Carusano, George Reins, Ryan Nielsen

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