Rheology as a survey tool: We are not there yet !

Stijn Claeys Thomas Van Hoestenberghe

Vessel MudContact

“Feeling the mud“= Based on reaction forces of mud exerted on the vessel

when trying to sail through it

Direct contact

Induced influence triggered by hydrodynamic activity

(internal wave)

Nautical bottom detection by density

Density – related? - resistance

“Hard bottom”

Top of sludge

Nautical bottom

reaction forces

Buoyancy Stickiness

Rheology

Deformation

“dull or sharp shape”: => different exerting forces

A small point of contact, magnifying the force ! Knowing

the shape parameters = knowing the applied force.

Density difference; volume Shape parameter

Rheology: “Resistance against deformation” (breaking mud

structures):•7 parameters to map the

rheology of the mud (Toorman)

•Thixotrophy: viscosity (read “structure of the mud”) is

⇒ time depending & deformation depending

= depending on the applied deformation and the history of

the applied deformation

Roughness; surfaceDispersive adhesion properties of mud

Other:Hydrodynamics during sailing

(currents around the hull, propeller action etc…)

Very complex => Nautica

Bearing capacity

Sampling & laboratory

Acoustical

Measuring principles

Mechanical Gamma

Optical

Field test = difficult=> Tested in the (Mud) Sludge Test Tank

Gas cleaner: odour

Sludge selection reservoir

Pumpreservoir

Hydro cyclone

Bridge with mixing/jetting

device

Aeration

Sampling and

observation

Measuring mud properties

Laboratory protocol

Mechanical based instruments= “feeling the mud”

towing

Towed body

vibrating

Tuning fork

“Staying on a level in the mud” = “viscous drag”

‘Staying’ on a rheological transition (RT) level? ⇒ “if” staying on RT is this the nautical bottom level?

⇒ cutting the nautical bottom mud? ⇒ ‘staying’ because of buoyancy?

⇒ friction due to dispersive adhesion in the mud?

Success => Controlled design: * towing speed; * design: shape parameters

* density of device= controlled applied shear stress + applied shear rate

Force needed to maintain the applied

chosen vibration ( shear rate = vibrating

frequency)

The restriction of the method is bound to a good calibration => need to seek the correct position on the

shear stress-shear rate rheogram

Info onmud column

Lateral 1 level info

Mechanical interaction

Type of instrument

Towed body <= reaction forces => vessel

rotating decelerating

rheometer free fall cone penetration test

(FF CPT) (cable burial, deep sea trenching)

“Measuring the shear-stress evolution in depth (not in time)”

Maintain the applied shear rate

-Automatic electronic torque compensation and thereby continuous registration of the torque

(rotating a rod).

-Measure the shear-stress info for a chosen applied deformation during profiling.

-No rheogram because of profiling speed

(resolution, “no time”), but possible = function (rotating speed, torque, shear rate)

= function of the shape rotating rod

“Deceleration due to differences in mud properties”

⇒‘slowing down’ on a rheological transition (RT) level? ⇒ “if” feeling a RT is this the nautical bottom level?

⇒ RT present? RT temporarily !

⇒ free fall profiling speed = deformation speed, depth depending (sensitivity of deceleration sensor)

⇒ ‘slowing down’ because of buoyancy? ; Friction due to dispersive adhesion in the mud?

Success => Controlled design: * profiling speed; * design: shape parameters

* density of device

Info onmud column Info on

mud column

Mechanical based instruments = “feeling the mud”

profiling tubeMechanical interaction

Type of instrument

Free fall body <= reaction forces => vesselRheometer In-situ => rheometer laboratory

Can we feel the mud ?

Range of low viscosities !•soil (high rigidity) => OK

•mud (very low rigidity) => ?

Thixotrophy !Deformation is depending on the applied

force. Deformation = changing the structure

=> changing viscosity” (dynamics viscosity)

⇒Time depending:Prehistory (passes vessels, dredging)

Mechanical = destructive

method: “disturbing the

mud”

Tuning

Towing Different shear rates due to:different shape parameters

* Hull* Rudder

* Propeller-sailing speed/ rotation speed

-contact surface (roughness, size)

Different mud behaviour because of:

-The viscosity of the mud is depending on the applied

deformation and time (thixotrophy):

⇒different parts of the passing vessel at different

time (hull, propeller, rudder)⇒ history of other passing

vessels (history of the applied deformation)

Measuring deviceVessel

= Mechanical

Mec

hani

cal

Deceleration

Different application scale

Rotating

Sampling & laboratory

Acoustical

Gamma

Optical

DIRECT LINK ? Yes, but not defined =>

physical model, mathematical model, CFD

Research

= Non-mechanical

Translation into rheology (if possible) & Calibration

DIRECT LINK ? Yes, but not defined =>

physical model, mathematical model, CFD

Extra difficulty Level / possible?

Non-DIRECT LINK

ResearchMainly based on density

Research (*)

CFD

RelateVessel-Mud

Labo-protocol

Field-protocol

Defining “the” rheology Parameters

Mud research: Historical, recent and new

Laboratory and Sludge Test Tank. “Micro scale”

Nautical research: Historical, recent and

new Physical and scale

model, 3D simulation. “Macro scale”

Computational Fluid Dynamics:

Step by step•1D => 2D => 3D

•Simple body => complex body => vessel

•1 layer => more layers•Different viscosities

•Non thixotrophic material => thixotrophic mud

& and the mix of the above

In-situ measuring protocol

“Nautical bottom”

(*)(2) Core research

or(2) more pragmatic ?

(1) Defining the parameters or

(2) defining a relative rheological

transition level

Field

Map the mud parameters

We are not there yet !

Rheology as a nautical survey tool

Continuing using density (different type of instruments)

combined with a safe keel-clearance

Density sensors: tested in the STT-Port of Rotterdam

-Rijkswaterstaat-MDK

-Consultancy (The Netherlands, Germany)

Paper availablestijn.claeys@mow.vlaanderen.be

Towing or profiling

Towing Profiling

⇒1 depth level => 1 parameter related ⇒Multiparameters possible

⇒Staying on a level =f(speed); control? ⇒Penetration in the mud =f(shape; weight, density, profiling speed)

⇒Long cable: free space needed: -Sailing straight lines, high currents?-Corners ?-Positioning (far away from vessel = reference)?-Measurements between moored vessels against quay-walls ?

⇒ Staying on position or fast profiling

⇒ Close to the vessel (= reference) (vertical profile depending on currents)

⇒Between moored vessels=f(usability of instrument: weight, staying in the water between the profiling; e.g. free-fall winch)

⇒No information about under- and above laying sediment

Dredging calculation purposesSafety purposes (different if mapped layer is nautical bottom or hard bottom)

⇒Resolution =f(data-collection speed)

⇒Resolution =f(amount profiles/time)

⇒Resolution =f(profiling speed)

•Info on “whole” mud column

Before the high resolution vertical profiling, towing was preferable.