Rheological parameters

Christof Baum

ALFRED WEGENER INSTITUTE FOR POLAR AND MARINE RESEARCH in the Hermann von Helmholtz Association (HGF)

Biophysical properties of the dolphin skin reveal an eco-friendly

defouling cycle

The biomimetic potential

of Bingham fluids

Rheological parameters

stress τ ↔↔ deformation γ

plate cone

γ = tan α

α

plate cone

Real-time rheology

stress τ [Pa]

0,1 1 10 100 1000 10000

deformation γ [-]

0,0001 0,001 0,01 0,1 1 10 100 1000

0,0057°

0,5729°

45,000°

84,280°

89,427°

5,7105°

0,0572°

89,942°

Dolphin facts

‹

Dolphin skin surface

‹ Gel covered

‹ Intercellular glycoproteins

‹

Transformation:

… fluidal state →→ visco-elastic solid …

… solid state →→ irreversible cohesive failure

‹

Yield point, σ

= 3-8 x 10

Pa

Bingham equation σ = σ_yield + η_p Á

Stress parameters

‹

Swimming (3-8 m/s)

20-80 Pa*

*J. Rohr et al., Journal of Experimental Biology 1998, 201, 1447–1460

‹

Jumping

3-8 x 10

Pa

‹ ≥

3-8 x 10

Pa definitely barnacle-free !

Stress at a barnacle base plate

Does the stress exceed the limit of cohesive failure at swimming speed 3-8 m/s ?

barnacle base plate

*Schultz et al., Biofouling 1999, 13, 323-335

Stress – Velocity – Correlation*

mean stream velocity [m/s]

0,1 1 10

stress [Pa]

at the base of a barnacle

10⁰ 10¹ 10² 10³ 10⁴ 10⁵ 10⁶ 10⁷

mean stream velocity [knots]

1 10 100

shear stress τ tessile stress σ

Basic equation of defouling

σ _non-fouled < σ _yield < σ _fouled

Bio-cycle → Bingham Fluids

Irreversible cohesive failure of the

covalently cross-linked gel perpetual renewal of skin

Biomimetic transformation

Reversible cohesive failure of the Bingham Fluid

thickness of the fluid

Application notes

nanoparticles

- modified silica

or TiO

… polymer base

- vaseline or silicone

oil …

… bio-organics ?

Field tests

‹ Seismic surveys (Morocco and Brazil)

– Coating seismic streamer cables

Barnacle-free streamer cable

‹ 2.5 - 3 month

‹ but seawater C° !

‹ … pending patent*

*AWI + Veritas Geophysical DGC PCT/ DE2004/ 000299

Future requirements

‹ Focus on the wall shear stress of marine constructions

‹ Measurements on drag and lift

‹ Evaluation of non-toxic impact

‹ New markets