Ludovic Chatellier

An experimental study on fish-friendly trashracks – Part 2. Angled trashracks

Experimental results for fish-friendly trashracks placed in an open water channel are presented. Model trashracks with different bar shapes, spacing and angles were tested. The numerous configurations provided results on head losses and on changes in velocity along the rack for a large range of situations, including fish-friendly trashracks. Previous head-loss equations found in the literature were applied to these configurations and were compared with measurements. A new head-loss equation is proposed that takes into account the effect of the different tested parameters. Velocity measurements provided new results and answers concerning downstream-migration aspects such as admissible approach velocities and guidance efficiency as a function of the trashrack angle.

Streamwise bars in fish-friendly angled trashracks

Experimental results for fish-friendly trashracks placed in an open-water channel are presented. Eighteen angled trashracks were used to test different bar spacings, bar shapes and rack angles. Each model trashrack comprised two horizontal supports with regularly spaced slots adjusted to compensate for the trashrack angle, i.e. maintain the vertical bars “streamwise” (parallel to flow). Water depths and velocity profiles were acquired upstream and downstream of each rack configuration. The results reveal that the head-loss coefficient for angled racks with streamwise bars does not depend on the rack angle and can be calculated with equations for racks perpendicular to the channel. Upstream velocity profiles along the rack are not significantly affected by the rack angle and downstream transverse profiles are nearly uniform. A comparison with conventional angled trashracks with bars set perpendicular to the rack revealed the many advantages of streamwise bars.

Spectral analysis of ship waves in deep water from accurate measurements of the free surface elevation by optical methods

This paper details the spectral analysis of the waves generated from an experimental study of the water surface elevation around a ship model in a towing tank. The wave pattern is measured with accurate optical methods in deep-water conditions for various Froude numbers. These optical methods allow the entire wave field around the model with a high spatial resolution to be obtained. The quality of the measured surface elevation around the ship model enables us to perform a spectral analysis of the waves generated by a ship. To validate this approach, the experimental spectrum is compared to the fundamental theoretical dispersion relation of the waves generated by a moving perturbation in calm deep water. In a second step, a fundamental decomposition of the wave system is achieved, from which the contribution of the near field, the local flow disturbance, and the contribution of the far field that corresponds to the Kelvin wake system are computed. In addition, the experimental extraction of the dispersion...

Maximum likelihood estimation of missing data applied to flow reconstruction around NACA profiles

In this paper, we investigate the maximum likelihood estimation for missing data in fluid flows series. The maximum likelihood estimation is provided with the expectation-maximization (EM) algorithm applied to the linear and quadratic proper orthogonal decomposition POD-Galerkin reduced-order models (ROMs) for various sub-samplings of large data sets. The flows around a NACA0012 profile at Reynolds numbers of 103 and angle of incidence of and a NACA0015 profile at Reynolds numbers of 105 and angle of incidence of are first investigated using time-resolved particle image velocimetry measurements and sub-sampled according to different ratios of missing data. The EM algorithm is then applied to the POD ROMs constructed from the sub-sampled data sets. The results show that, depending on the sub-sampling used, the EM algorithm is robust with respect to the Reynolds number and can reproduce the velocity fields and the main structures of the missing flow fields for 50% and 75% of missing data.

Closure to “An experimental study on fish-friendly trashracks: part I & II”

The Authors thank the Discussers for their observations on our two papers. Four main points, related to head-loss predictions for angled trashracks, have been underlined by the Discussers and are discussed here.[...]