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Development of a wave flume for the centrifuge. Dr Tim Newson / Dr Ping Dong University of Dundee. Geo-fluids Research Group. Academic staff Dr. T.A. Newson Dr. P. Dong Dr M.F. Bransby Professor Kenichi Sato Professor M.C.R. Davies Research interests

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development of a wave flume for the centrifuge

Development of a wave flume for the centrifuge

Dr Tim Newson / Dr Ping Dong

University of Dundee

slide2

Geo-fluids Research Group

Academic staff

  • Dr. T.A. Newson
  • Dr. P. Dong
  • Dr M.F. Bransby
  • Professor Kenichi Sato
  • Professor M.C.R. Davies

Research interests

Coastal engineering, offshore engineering, in situ testing, numerical modelling, constitutive modelling, centrifuge modelling, element tests

slide3

Requirements for Appropriate Scaling in Physical Modelling

  • Requirement for similitude between material properties in prototype and model
  • Stress-strain behaviour of geomaterials is highly non-linear, stress level dependent and stress history dependent
slide5

Gravity stress

Gravity stress

g

‘nth’ Scale Model

g

Prototype

hm

hp

Depth

Depth

Stress Similitude in Model & Prototype

slide6

Inertia stress

w

w2. r

Gravity stress

g

‘nth’ Scale Model

Prototype

hm

hp

Depth

Depth

Stress Similitude in Model & Prototype

slide7

prototype:

p

hp

g



m

model:

(ng) 



hp

g

hp

n

i.e.

p = m

Stress Similitude in Model & Prototype

acceleration = r x  = n.g

slide8

Centrifuge Modelling Laws

- Defined Quantities

Physical quantity

Prototype

Model

Macroscopic length

1

1/n

Stress

1

1

Strain

1

1

Pore water pressure

1

1

Time :

1

2

diffusion processes

1

1/n

inertial effects

1

1/n

2

Force

1

1/n

Interstitial water velocity

1

n

Heat flux

1

n

slide9

Centrifuge modelling

Drum centrifuge

Fixed beam centrifuge

slide10

Wave flumes on the centrifuge

50 g tests, 4m water depth, 4.5 m sand

Sekiguchi et al. (2000)

Viscous pore fluid - simultaneous scaling of consolidation & inertia

slide11

Centrifuge modelling

Ultrasonic generator

Wave Paddle

Slotted partition

Strong box

Fluid

250 mm

PWP transducers

Soft soil

550 mm

slide12

Standing wave

Progressive wave

Anti-node

Slotted partition

Node

Centrifuge modelling

Wave Paddle

Fluid

PWP transducers

Soft soil

slide13

Progressive waves (co = 0.13)

Sub-liquefaction behaviour

umax = 4 kPa

slide14

Standing waves (co = 0.20)

Liquefaction behaviour

umax = svo’

slide16

Post wave loading behaviour

Post wave pore pressures

Surface settlement

slide17

Theoretical Basis

Wave surface elevation

where S0 is the displacement of the board at the water level

The dispersion relationship

where

slide18

Wave pressure at flume base

Amplitude of wave pressure

slide19

Limitations

1. The real soil is not an ideal poro-elastic body

2. The theoretical model is applicable to semi- infinite soil, but the model soil in the centrifuge is of finite depth.

3. The influence of structures is not accounted for

4. Particle movement not accounted for

slide20

Scaling factors in centrifuge

Basic parameters

Acceleration g: N

Model length scale, H, h, etc: 1/N

Prototype soil materials used in the model

Density ρ: 1

Particle size d: 1

slide21

Scaling factors in centrifuge

Derived parameters

Wave period T: 1/N

Wave number k: N

Fluid pressure: 1

Fluid flow velocity: 1

Inertia time scale: 1/N

Laminar flow time scale: 1/N2

By using pore fluid with a high viscosity (N times higher) such as silicone oil, the laminar flow scale can be made to be 1/N

slide22

Paddle Design

Dimensions of the strong box

Japan Dundee

(Sekiguchi et al. 1998)

Length (mm) 550 1600

Height (mm) 250 680

Width (mm) 100 276

Wave generator Quasi-Flap Type Quasi-Flap Type

slide24

Paddle and operation

(1) AC servo motor (4) Crank shaft

(2) Reduction wheel (5) Wave paddle

(3) Attachment wheel (6) Wave channel

slide25

Typical operating conditions

Japan Dundee

Wave height: 10-23 mm 5-40 mm

Wave frequency: 11 Hz 5-15 Hz

Water depth: 90 mm 100-300 mm

Sand bed thickness: 100mm 100-200mm

Centrifugal accel.: 50 25-50 (? less)

slide26

Applications / Collaboration

  • Validation against large flume data
  • Validation/calibration of numerical models
  • Different soils: sand/silt/clayey/gassy?
  • Small structures: cylinder/sphere/cube (surface & buried)
  • Large structures: caisson/breakwater/cliff