FN Archimer Export Format
PT J
TI Behaviour of a floc population during a tidal cycle: laboratory experiments and numerical modelling
BT 
AF VERNEY, Romaric
   LAFITE, Robert
   BRUN-COTTAN, Jean Claude
   LE HIR, Pierre
AS 1:1;2:2;3:3;4:1;
FF 1:PDG-ODE-DYNECO-PHYSED;2:;3:;4:PDG-ODE-DYNECO;
C1 IFREMER, Lab Dyneco Physed, F-29280 Plouzane, France
   Univ Rouen, UMR CNRS M2C 6143, F-76821 Mont St Aignan, France
   Univ Caen, UMR CNRS M2C 6143, F-14000 Caen, France
C2 IFREMER, FRANCE
   UNIV ROUEN, FRANCE
   UNIV CAEN, FRANCE
SI BREST
SE PDG-ODE-DYNECO-PHYSED
   PDG-ODE-DYNECO
IN WOS Ifremer jusqu'en 2018
   copubli-france
   copubli-univ-france
IF 2.088
TC 75
UR https://archimer.ifremer.fr/doc/00027/13846/11020.pdf
LA English
DT Article
DE ;Flocculation;Tidal cycle;Laboratory experiment;FLOCMOD;OD model;Sensitivity analysis;Optimization
AB An approach combining laboratory experiments and numerical modelling was used to investigate the behaviour of a floc population during an idealized tidal cycle. The experiment was conducted on suspended sediments at a concentration of 93 mg l−1 collected in the field. It was based on a jar test device to reproduce tidal-induced turbulence and coupled with a CCD camera system and image post-processing software to monitor floc size distribution. At the same time, a 0D size-class based aggregation/fragmentation model (FLOCMOD) was developed to simulate changes in the floc population over the tidal cycle. Experimental results revealed strong variability of the behaviour of microfloc and macrofloc populations with respect to the varying shear rates observed in situ. In particular, the major dependency of floc sizes on the Kolmogorov microscale was confirmed. Time-scale differences were also observed for aggregation and fragmentation processes which led to asymmetrical floc behaviour despite symmetrical tidal forcing. Model results, i.e. average diameter, maximum diameter and floc size distribution, were in good agreement with experimental data with an RMS error between observed and computed average diameters of below 25 μm over the tidal cycle.  FLOCMOD was optimized in terms of the time step, number of size classes and size range: only seven classes ranging from 50 to 643 μm associated with a dynamically-adaptable time step were needed to correctly reproduce experimental results, characterized by an RMS error of less than 5 μm with respect to the reference case (100 classes from 4 to 1500 μm).  Sensitivity analyses were performed on major parameters or processes: initial floc size distribution, primary particle size, fractal dimension and fragmentation function (binary, ternary, erosion or collision-induced fragmentation). Results showed that initial floc size distribution played a role only during the first aggregation stage. Low variability of the fractal dimension did not significantly modify model results, while larger differences were observed when the primary particle size was changed, especially towards the largest sizes (10 μm). Nevertheless, these two structural parameters had a strong impact on the calculated mean settling velocity with differences of 0.2 mm s−1 compared with the reference case.  Different fragmentation functions were shown to significantly modify model results, except for collision-induced shear stress. In particular, combining floc erosion with binary breakup in the shear fragmentation term enabled us to reproduce bimodal distributions, patterns that are typically observed in situ.
PY 2011
PD JUN
SO Continental Shelf Research
SN 0278-4343
PU Pergamon-elsevier Science Ltd
VL 31
IS 10
UT 000293319700007
DI 10.1016/j.csr.2010.02.005
ID 13846
ER

EF