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Two pelagic otterboards, previously tested in a wind tunnel, have been tested in a flume tank prior to their analysis in real working conditions in sea trials. This intermediate step aims at providing guidance for sea trial planning and a basis for otter board performance analysis from real campaign data. The doors were rigged in working-like conditions in the flume tank, with onboard-mounted attitude sensors to provide at the same time a noisy environment as expected in sea trials and accurate measurement of all quantities relevant to precise determination of hydrodynamic angles and forces. The trends found in flume tank experiments closely match wind tunnel results, although systematic offset has been observed that can be ascribed to deviations between nominal and real water velocity, due to inhomogeneous velocity distribution in the cross-section. [ABSTRACT FROM AUTHOR]

The feasibility and potential advantages of wind tunnel testing of otter board designs are assessed. Traditional flume tank tests incur high operational costs and present some limitations in terms of flexibility and accuracy. Modern flume tanks, despite more flexible and accurate, are still expensive to operate or hire. Wind tunnel facilities are widespread, with a potential for low budget tests, and allow for an accurate control of velocity, angle of attack and sideslip as well as precise measurement of forces and moments in all three axes. A complete description of otter board hydrodynamics is paramount to optimising design and rigging and for the design of active control strategies that allow for stable trawling at a target speed and depth. We describe in detail the methodology of wind tunnel tests applied to general otter board designs, exemplify it with a commercial pelagic otter board and provide a comparison with existing flume tank results for the same design. [ABSTRACT FROM AUTHOR]

Different dynamic operating behaviors of a continuous ethanol fermenter evidenced from bifurcation analysis and exhibited in a two-parameter continuation diagram (feed substrate concentration (S f) vs dilution rate parameter (D)). [Display omitted] • The dynamic behavior of a continuous fermentor was predicted by bifurcation theory. • The combination of arc-length continuation method and Heaviside function is detailed. • An oscillatory envelope of state variables was exhibited at a wide parameters range. • Bifurcation diagrams reveal the suitable conditions for continuous fermentation. The oscillatory behavior of a continuous ethanol fermentor, in the high feed sugar concentration region (200 g/L), is analyzed using the bifurcation theory. The mathematical model was solved using the arc-length continuation method including a refinement algorithm based on the Heaviside step function technique. Experimental data for ethanol production using Zymomonas mobillis were fitted to a phenomenological model based on the concept of dynamic specific growth rate and inhibition. Thus, a through connection is defined between model parameters and oscillatory behavior. Our approach shows the rich static and dynamic bifurcation topology of the continuous fermentation reactor, which includes Fold, Hopf, Bautin, and Cusp bifurcations. The four-dimensional model shows that intricate oscillations can occur and that the periodic attractors of the system can have thoughtful consequences on reactor performance. In fact, it is evidenced that, in some conditions, periodic/bifurcation behavior presents higher ethanol productivity than the corresponding steady-state. Bifurcation analysis provides insight into the possible operation conditions and their impact on conversion and productivity of the fermentation process. [ABSTRACT FROM AUTHOR]