Creating underwater vision through wavy whiskers: a review of the flow-sensing mechanisms and biomimetic potential of seal whiskers

Seals are known to use their highly sensitive whiskers to precisely follow the hydrodynamic trail left behind by prey. Studies estimate that a seal can track a herring that is swimming as far as 180 m away, indicating an incredible detection apparatus on a par with the echolocation system of dolphins and porpoises. This remarkable sensing capability is enabled by the unique undulating structural morphology of the whisker that suppresses vortex-induced vibrations (VIVs) and thus increases the signal-to-noise ratio of the flow-sensing whiskers. In other words, the whiskers vibrate minimally owing to the seal's swimming motion, eliminating most of the self-induced noise and making them ultrasensitive to the vortices in the wake of escaping prey. Because of this impressive ability, the seal whisker has attracted much attention in the scientific community, encompassing multiple fields of sensory biology, fluid mechanics, biomimetic flow sensing and soft robotics. This article presents a comprehensive review of the seal whisker literature, covering the behavioural experiments on real seals, VIV suppression capabilities enabled by the undulating geometry, wake vortex-sensing mechanisms, morphology and material properties and finally engineering applications inspired by the shape and functionality of seal whiskers. Promising directions for future research are proposed.

Transverse FIV suppression of square cylinder using two control rods of varying size and distance in lock-in and galloping regions

Purpose) In this study, for the first time, the efficacy of control rods for full suppression of vortex-induced vibrations (VIV) and galloping of an elastically supported rigid square cylinder that vibrates freely in the cross-flow direction is investigated. Design/methodology/approach To this aim, two small control rods are placed at constant angles of ± 45° relative to the horizontal axis and then the influence of diameter and spacing ratios on the oscillation and hydrodynamic response along with the vortex structure behind the cylinder is evaluated in the form of nine different cases in both VIV and galloping regions. Findings The performed simulations show that using the configuration presented in this study results in full VIV suppression for the spacing ratios G/D = 0.5, 1 and 1.5 at the diameter ratios d/D = 0.1, 0.2 and 0.3 (D: diameter of square cylinder, G: distance between rods and cylinder, d: diameter of rods). On the contrary, a perfect attenuation of galloping is only achieved at the largest diameter (d/D = 0.3) and the smallest spacing ratio (G/D = 0.5). In general, for both VIV and galloping regions, with increasing diameter ratio and decreasing spacing ratio, the effect of the control rods wake in the vortex street of square cylinder gradually increases. This trend carries on to the point where the vortex shedding is completely suppressed and only the symmetric wake of control rods is observed. Originality/value So far, the effect of rod control on VIV of a square cylinder and its amplitude of oscillations has not been investigated.

Fully Turbulent Vortex-Induced Vibration on a Cylinder Structure With a Nonlinear Energy Sink Absorber

The fully turbulent vortex induced vibration (VIV) suppression of a circular cylinder through a nonlinear energy sink (NES) having linear damping and nonlinear cubic stiffness is investigated numerically. The computational fluid dynamics (CFD) method is carried out to calculate the fluid field, while a fourth-order Runge-Kutta method is used to calculating the nonlinear structure dynamics of flow-cylinder-NES coupled system. The fluid-structure interaction (FSI) model is validated against VIV experimental data for a cylinder in a uniform flow. The simulation results show that placing an NES structure with suitable parameters inside of the cylinder structure achieves a good VIV amplitudes’ suppression effect and narrows the “lock-in” region.

Field Trial of Vortex-Induced Vibration Suppression Technology for Drilling Riser Buoyancy

Instrumented field trials of Longitudinally Grooved Suppression (LGS) VIV suppression buoyancy modules have been completed on deep water drilling risers in the Gulf of Mexico. The field trials were used to validate the performance of the technology, which had previously been evaluated using prototype scale model tests. The measured riser responses over two drilling campaigns spanning more than six months were compared with each other and the outputs of computational riser modeling to validate the hydrodynamic parameter set derived through scale model tests and provide validated assessments of the suppression technology performance. The measured response of drilling risers equipped with LGS buoyancy has been compared with a publicly available dataset for the VIV response of a conventionally buoyed riser, showing reduced VIV response in agreement with model test results. Measured flex joint angles, current profiles and riser accelerations were used to validate the hydrodynamic parameters used in numerical riser analysis. Using the validated hydrodynamic parameters, the VIV and drag suppression performance was demonstrated by comparison with the model predictions for risers equipped with conventional buoyancy modules. Eddy current occurrence statistics for a location in the Gulf of Mexico were used to calculate the expected annual operability performance for both configurations. For the base case parameters, 12 days of annual operability improvement was predicted when using LGS buoyancy modules. A sensitivity study determined the effect of varying analysis assumptions on the predicted operability improvements. Measured current data from 2014 was also used to determine the operability benefits which could be realized within a year in which severe eddy current activity occurred. The analysis performed serves to validate the previous laboratory tests as well as answer questions about the applicability of high Reynolds Number test results to VIV suppression devices in the field. The use of previously validated testing and analysis methods is shown to provide reliable estimates of suppression technology performance which are borne out by testing in the field. This paper presents the first published field trial of shaped buoyancy type VIV suppression, a group of technologies which have until now only been demonstrated using scale model tests and Computational Fluid Dynamics simulations.