3.4. Experiments using digital holography for PIV

Figure 12 shows the hologram reconstruction of a spherical particle of 50 μm. Figure 12a shows the particle's hologram already filtered, where the different patterns of diffraction are observed; Figure 12b provides greater detail. The relative intensity profile (I/Imax) vs. reconstruction distance (z) is shown in Figure 12c. The maximum intensity is shown where the particle is in focus.

Figure 13a shows the digital hologram of flocs, while Figure 13b shows a preprocess in order to avoid noise in the hologram. Rings of interference are observed in both figures, which define the 3D characteristics of the flocs. Figure 13c shows the reconstruction of the binary image. This image only shows the particles that are in the best focus, i.e., where the shape of the particle is clearly defined. In order to find the position in the plane, the diameter, and shape of


Figure 10. Primary particles and flocs representative of the Grijalva river.

124 Applications in Water Systems Management and Modeling

Figure 11. Primary particles and flocs representative of the Usumacinta river.

Figure 12. Results of a reconstruction of hologram process. (a) Originally filtered hologram; (b) one particle hologram; (c) relative intensity profile, and (d) reconstructed particle.

the particle, the PTV algorithm for non-spherical particles was applied. Figure 13d shows particles pair detection and its centroid, which allows us to determine particles' velocity for a sequence of holograms.

4. Conclusions

toward the recirculation deposit.

amount of cohesive sediments.

Author details

References

Klever Izquierdo Ayala

A model to estimate the floc settling velocity was calibrated for flocs obtained from aquaculture recirculation tanks that cultivate trout. The model was able to reproduce the values of settling velocity which varies between 0.01 and 0.025 m/s. For all the recording times analyzed

Optical Methods Applied to Hydrodynamics of Cohesive Sediments

http://dx.doi.org/10.5772/intechopen.72347

127

The representative values of the parameters used to determine fractal dimension are proposed in this research according to the experimental results. These values depend on floc density and vary with experimental time as flocs become more porous. The values found in this research

The practical findings for aquaculture recirculation tanks design is that residence times should be short in order to minimize the presence of very large flocs. Middle size flocs settle faster. In designing the central settling device, which functions according to the hydrociclons principle, the up flow velocity should be less than 0.01 m/s in order to diminish the flow of sediments

A method to obtain the suspended sediment concentration profiles for rivers with mainly cohesive sediments was presented. It is necessary to take some representative samples and using a rotating annular flume defines a steady state of flocculation after long-term runs. The most suitable method to analyze size and settling velocity of flocs are optical methods, PTV and microscopy. This research shows that the settling velocity can be accurately calculated with Eq. (6) in order to obtain an appropriate estimation of the Rouse number ZR. This allows us to properly determine the suspended sediment concentration profiles in rivers carrying a large

Non-intrusive optical techniques are a suitable tool to characterize cohesive sediments, because they do not destroy flocs and allow for microscopic analysis. More advanced optical methods, like DHPIV, are showing good results for floc size and shape determination, thus in

the future they will be the best method for cohesive sediment analysis.

\*Address all correspondence to: jagarciaa@uaemex.mx

Juan Antonio Garcia Aragon\*, Salinas Tapia Humberto, Diaz Palomarez Victor and

CIRA-Faculty of Engineering, Universidad Autónoma del Estado de México, Toluca, Mexico

[1] Bouchez J, Metivier F, Lupker M, Maurice L, Perez M, Gaillardet J, France-Lanord C. Prediction of depth-integrated fluxes of suspended sediment in the Amazon River: Parti-

cle aggregation as a complicating factor. Hydrological Processes. 2011;25:778-794

there is a maximum settling velocity for flocs of diameter of 600 μm.

apply to flocs coming from trout cultures in high level locations, i.e., 2800 masl.

A settling column was used in order to observe the hologram evolution over time. Almost 100 holograms were processed each recording time. The times recorded were t = 0, 10, 20, 30, 45, and 60 min. Figure 14a shows particles distribution for holograms at time t = 0, and it can be observed that maximum size is 160 □m, with a mean diameter of 70 □m.

Figure 14c shows the distribution of particles at time 30 min, where an increase in size of flocs is observed attaining a maximum of 180 □m and a mean value of 80 □m. It is also observed that the shape of the distribution is log-normal, similar to theory. Figure 14d shows clearly a nonuniform distribution of particles in a hologram.

Figure 13. Results of analysis of a digital hologram. (a) Original digital hologram; (b) processed digital hologram; (c) reconstructed hologram, and (d) size and shape of detected particles.

Figure 14. Characteristics of flocs in settling column (a) frequency distribution of sizes at t = 0 min; (b) spatial distribution of flocs at t = 0 min; (c) frequency distribution of sizes t = 30 min; (d) spatial distribution of flocs at t = 30 min.
