DOLPHIN-INSPIRED COMPLIANT COATINGS FOR DRAG … Stuebing.pdfDolphin skin Model: Flexible membrane as dermis, spring-damper system as blubber → Parameters:Spring and damper rates,

© Fraunhofer The 19th International Congress on Marine Corrosion and Fouling June 24-29, 2018 | Melbourne, Florida

DOLPHIN-INSPIRED COMPLIANT COATINGS FOR DRAG REDUCTION OF SHIPS

Dorothea Stübing, Volkmar Stenzel, Claus Schreiner; Fraunhofer IFAM Lars-Uve Schrader; Hamburg Ship Model Basin - HSVA

©SaveJapanDolphins.org

Dorothea Stübing

19th ICMCF June 2018

Fraunhofer IFAM


Hydrodynamic champions in nature

Different strategies to optmize hydrodynamics

Sharks – micro-textured skin Reduction of turbulent skin friction

Penguins – air lubrication Reduction of turbulent skin friction

Dolphins – compliant skin Retention of laminar flow

©WallPaperSite.com

©National Geographic

Source: youtube

Dorothea Stübing


Fraunhofer IFAM


The biological example and the technical model

Dolphin skin

Model: Flexible membrane as dermis, spring-damper system as blubber

→ Parameters: Spring and damper rates, bending stiffness

reproduced after www.oceanbites.org reproduced after Carpenter & Garrad, J. Fluid Mech. 155, 1985

Dorothea Stübing


Fraunhofer IFAM


FLIPPER – background of the project

Increase of resistance at

transition from laminar to

turbulent friction

Coefficient of friction vs. Reynolds number for flow over a flat plate

Source: Lecture “Bionik I” Winter 00/01 - Ingo Rechenberg, TU Berlin

Dorothea Stübing


Fraunhofer IFAM


Background of the project

Laminar-turbulent transition along the streamlines

Simplified representation by Hamburgische Schiffbau-Versuchsanstalt GmbH (HSVA)

Delayed transition → significant effect on resistance

Dorothea Stübing


Fraunhofer IFAM


Approach of the project

Shear stress on the hull (vessels without bulbous bow)

Maximum shear stress on the bow → Flexible bow coating

Laminar behavior of the boundary layer → delay of the transition to turbulence

Dorothea Stübing


Fraunhofer IFAM


Approach of the project

Delay of transition point increase of laminar flow reduction of resistance

Mechanistic hypothesis: If damping of the T-S waves enables energy to be removed from the

boundary layer, then the laminar-turbulent transition should be delayed New polymers having extremely good energy dissipation should be ideal for

this purpose

T-S waves

Delay of transition from laminar to turbulent friction

Dorothea Stübing


Fraunhofer IFAM


Work plan

HSVA Identification of the relevant hydrodynamic data and required material parameters by analytical methods and numerical simulation

IFAM Selection of appropriate materials, formulation of damping coating systems optimized for the hydrodynamic conditions

HSVA + IFAM Construction of a demonstrator for experimental validation of the drag reduction potential

HSVA Hydrodynamic testing

Dorothea Stübing


Fraunhofer IFAM


Material development I – high-damping polymer

Elastomeric rubber (Reverlink HM, Arkema)

dampens vibrations dampens noise dampens defined frequencies / frequency ranges

Relevant frequencies of T-S waves

Dorothea Stübing


Fraunhofer IFAM



Reverlink-based coating options

Damping polymer as main binder

Damping polymer as co-binder

Damping polymer as additive

(domain structure)

Pigment/Filler

Dorothea Stübing


Fraunhofer IFAM



Reverlink-based coating options

Damping polymer as main binder Damping polymer as additive in PUR-coating

Dorothea Stübing


Fraunhofer IFAM


Refined simulations identified different requirements on material properties High-damping material unsuitable due to generation of FISI waves

Stability map


Critical point = onset of T-S instability Dorothea Stübing


Fraunhofer IFAM


Principle of TS and FISI waves – banana diagrams

Dorothea Stübing


Fraunhofer IFAM


Principle of TS and FISI waves – banana diagrams

If too far away from optimum another challenge occurs:

Detrimental to hydrodynamic performance

Flow-Induced Surface Instabilities (FISI waves)

Dorothea Stübing


Fraunhofer IFAM


Required material parameters – ideal coating

Dorothea Stübing


Fraunhofer IFAM


Optmized material

[1/s]

0.1 1 10 100 1000

E' [

MP

a]

10

100

1000

[1/s]

0.1 1 10 100 1000

tan

[ ]

0.00

0.05

0.10

0.15

0.20

0.25

LDPE 0.16 mm

[1/s]

1 10 100 1000

tan

[ ]

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

AlpaGel/Köraform 50/50

[1/s]

1 10 100 1000

1

10

100

Relevant frequency range

Relevant frequency range

Blubber: AlpaGel/Köraform 50/50 Material parameters as per DMA measurements:

E-modulus: > 11.5 kPa (spec: 50 kPa) Loss factor: ~ 0.11 (spec: 0.05) Dermis: LD-PE film E-modulus: ~ 370 MPa at 160 µm (spec 200 MPa at 200 µm) Loss factor: ~ 0.115 (spec: 0.05)

E' [

kPa]

Dorothea Stübing


Fraunhofer IFAM


Hydrodynamic test campaign

Alpa-Gel/Köraform + PE film 1.

2.

3.

Bow segment (scale 1:3.2) – view of starboard side and stem 1. Rigid surface – standard coating 2. Flexible coating with blubber of 3 mm thickness 3. Flexible coating with blubber of 10 mm thickness

Dorothea Stübing


Fraunhofer IFAM


Hydrodynamic test campaign – results

Alpa-Gel/Köraform + PE film

Up to 6 % drag reduction at high flow velocities (10 m/s)

Dorothea Stübing


Fraunhofer IFAM


Summary and Outlook

Successful demonstration of drag reduction potential of dolphin skin concept Determination of optimum material parameters Identification of suitable materials Realization of demonstrator

Up to 6 % drag reduction

Outlook Optimization of the two material components (blubber and dermis) Graded approach for prolonged retention of laminarity beyond bow Integration of fouling control solution Adaptation to full-scale vessel and demonstration

Dorothea Stübing


Fraunhofer IFAM


Acknowledgements on behalf of the consortium

Many thanks for your attention!

Dorothea Stübing


Fraunhofer IFAM

Documents

DOLPHIN-INSPIRED COMPLIANT COATINGS FOR DRAG … Stuebing.pdfDolphin skin Model: Flexible membrane as dermis, spring-damper system as blubber → Parameters:Spring and damper rates,