Workshop we are not there yet 2


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Steijn Claes - on developments in rheology

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Workshop we are not there yet 2

  1. 1. Rheology as a survey tool: We are not there yet ! Stijn Claeys Thomas Van Hoestenberghe
  2. 2. Vessel Mud Contact “ 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
  3. 3. 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 <ul><li>Rheology: “Resistance against deformation” (breaking mud structures): </li></ul><ul><li>7 parameters to map the rheology of the mud (Toorman) </li></ul><ul><li>Thixotrophy: viscosity (read “structure of the mud”) is </li></ul><ul><li>time depending & deformation depending </li></ul><ul><li>= depending on the applied deformation and the history of the applied deformation </li></ul>Roughness; surface Dispersive adhesion properties of mud Other: Hydrodynamics during sailing (currents around the hull, propeller action etc…) Very complex => Nautica Bearing capacity
  4. 4. Sampling & laboratory Acoustical Measuring principles Mechanical Gamma Optical Field test = difficult => Tested in the (Mud) Sludge Test Tank Gas cleaner: odour Sludge selection reservoir Pump reservoir Hydro cyclone Bridge with mixing/jetting device Aeration Sampling and observation Measuring mud properties Laboratory protocol
  5. 5. Mechanical based instruments= “feeling the mud” towing Towed body vibrating Tuning fork <ul><li>“ Staying on a level in the mud” </li></ul><ul><li>= “viscous drag” </li></ul><ul><li>‘ Staying’ on a rheological transition (RT) level? </li></ul><ul><li>“ if” staying on RT is this the nautical bottom level? </li></ul><ul><li>cutting the nautical bottom mud? </li></ul><ul><li>‘ staying’ because of buoyancy ? </li></ul><ul><li>friction due to dispersive adhesion in the mud? </li></ul><ul><li>Success => Controlled design : </li></ul><ul><li>* towing speed; * design: shape parameters </li></ul><ul><li>* density of device </li></ul><ul><li>= controlled applied shear stress + applied shear rate </li></ul>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 on mud column Lateral 1 level info Mechanical interaction Type of instrument Towed body <= reaction forces => vessel
  6. 6. rotating decelerating rheometer free fall cone penetration test (FF CPT) (cable burial, deep sea trenching) <ul><li>“ Measuring the shear-stress evolution in depth (not in time)” </li></ul><ul><li>Maintain the applied shear rate </li></ul><ul><li>Automatic electronic torque compensation and thereby continuous registration of the torque (rotating a rod). </li></ul><ul><li>Measure the shear-stress info for a chosen applied deformation during profiling. </li></ul><ul><li>No rheo gram because of profiling speed (resolution, “no time”), but possible </li></ul><ul><li>= function (rotating speed, torque, shear rate) </li></ul><ul><li>= function of the shape rotating rod </li></ul><ul><li>“ Deceleration due to differences in mud properties” </li></ul><ul><li>‘ slowing down’ on a rheological transition (RT) level? </li></ul><ul><li>“ if” feeling a RT is this the nautical bottom level? </li></ul><ul><li>RT present? RT temporarily ! </li></ul><ul><li>free fall profiling speed = deformation speed, depth depending (sensitivity of deceleration sensor) </li></ul><ul><li>‘ slowing down’ because of buoyancy ? ; Friction due to dispersive adhesion in the mud? </li></ul><ul><li>Success => Controlled design : </li></ul><ul><li>* profiling speed; * design: shape parameters </li></ul><ul><li>* density of device </li></ul>Info on mud column Info on mud column Mechanical based instruments = “feeling the mud” profiling tube Mechanical interaction Type of instrument Free fall body <= reaction forces => vessel Rheometer In-situ => rheometer laboratory
  7. 7. <ul><li>Can we feel the mud ? </li></ul><ul><li>Range of low viscosities ! </li></ul><ul><li>soil (high rigidity) => OK </li></ul><ul><li>mud (very low rigidity) => ? </li></ul><ul><li>Thixotrophy ! </li></ul><ul><li>Deformation is depending on the applied force. </li></ul><ul><li>Deformation = changing the structure </li></ul><ul><li>=> changing viscosity” (dynamics viscosity) </li></ul><ul><li>Time depending: </li></ul><ul><li>Prehistory (passes vessels, dredging) </li></ul>Mechanical = destructive method : “disturbing the mud”
  8. 8. Tuning Towing <ul><li>Different shear rates due to: </li></ul><ul><li>different shape parameters </li></ul><ul><li>* Hull </li></ul><ul><li>* Rudder </li></ul><ul><li>* Propeller </li></ul><ul><li>sailing speed/ rotation speed </li></ul><ul><li>contact surface (roughness, size) </li></ul><ul><li>Different mud behaviour because of: </li></ul><ul><li>The viscosity of the mud is depending on the applied deformation and time (thixotrophy): </li></ul><ul><li>different parts of the passing vessel at different time (hull, propeller, rudder) </li></ul><ul><li>history of other passing vessels (history of the applied deformation) </li></ul>Measuring device Vessel = Mechanical Mechanical 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 Research Mainly based on density
  9. 9. Research (*) CFD Relate Vessel-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” <ul><li>C omputational F luid D ynamics : </li></ul><ul><li>Step by step </li></ul><ul><li>1D => 2D => 3D </li></ul><ul><li>Simple body => complex body => vessel </li></ul><ul><li>1 layer => more layers </li></ul><ul><li>Different viscosities </li></ul><ul><li>Non thixotrophic material => thixotrophic mud </li></ul><ul><li>& and the mix of the above </li></ul>In-situ measuring protocol “ Nautical bottom” <ul><li>(*) </li></ul><ul><li>Core research </li></ul><ul><li>or </li></ul><ul><li>(2) more pragmatic ? </li></ul><ul><li>Defining the parameters or </li></ul><ul><li>defining a relative rheological transition level </li></ul>Field Map the mud parameters
  10. 10. We are not there yet ! Rheology as a nautical survey tool Continuing using density (different type of instruments) combined with a safe keel-clearance <ul><li>Density sensors: tested in the STT </li></ul><ul><li>-Port of Rotterdam </li></ul><ul><li>Rijkswaterstaat </li></ul><ul><li>MDK </li></ul><ul><li>Consultancy (The Netherlands, Germany) </li></ul>Paper available [email_address]
  11. 12. Towing or profiling Towing Profiling <ul><li>1 depth level => 1 parameter related </li></ul><ul><li>Multiparameters possible </li></ul><ul><li>Staying on a level =f(speed); control? </li></ul><ul><li>Penetration in the mud </li></ul><ul><li>=f(shape; weight, density, profiling speed) </li></ul><ul><li>Long cable: free space needed: </li></ul><ul><li>Sailing straight lines, high currents? </li></ul><ul><li>Corners ? </li></ul><ul><li>Positioning (far away from vessel = reference)? </li></ul><ul><li>Measurements between moored </li></ul><ul><li>vessels against quay-walls ? </li></ul><ul><li>Staying on position or fast profiling </li></ul><ul><li>Close to the vessel (= reference) </li></ul><ul><li>(vertical profile depending on currents) </li></ul><ul><li>Between moored vessels </li></ul><ul><li>=f(usability of instrument: weight, staying </li></ul><ul><li>in the water between the profiling; e.g. free-fall winch) </li></ul><ul><li>No information about under </li></ul><ul><li>- and above laying sediment </li></ul><ul><li>Dredging calculation purposes </li></ul><ul><li>Safety purposes (different if mapped layer </li></ul><ul><li>is nautical bottom or hard bottom) </li></ul><ul><li>Resolution =f(data-collection speed) </li></ul><ul><li>Resolution =f(amount profiles/time) </li></ul><ul><li>Resolution =f(profiling speed) </li></ul><ul><li>Info on “whole” mud column </li></ul>Before the high resolution vertical profiling, towing was preferable.