Despite recent extensive research into fluid–structure interaction (FSI) of cavitating hydrofoils, there remain insufficient experimental data to explain many of the observed phenomena. The cloud cavitation behavior around a hydrofoil due to the effect of FSI is investigated, utilizing rigid and compliant three-dimensional (3D) hydrofoils held in a cantilevered configuration in a cavitation tunnel. The hydrofoils have identical undeformed geometry of tapered planform with a constant modified NACA0009 profile. The rigid model is made of stainless steel and the compliant model of a carbon and glass fiber-reinforced epoxy resin with the structural fibers aligned along the spanwise direction to avoid material bend-twist coupling. Tests were conducted at an incidence of 6 deg, a mean chord-based Reynolds number of 0.7 × 106 and cavitation number of 0.8. Force measurements were simultaneously acquired with high-speed imaging to enable correlation of forces with tip bending deformations and cavity physics. Hydrofoil compliance was seen to dampen the higher frequency force fluctuations while showing strong correlation between normal force and tip deflection. The 3D nature of the flow field was seen to cause complex cavitation behavior with two shedding modes observed on both models.
Characterising crustacean behaviour in response to conspecific chemical cues contributes to our evolving knowledge of the drivers of their social behaviour. There is particular interest in understanding the chemical and behavioural mechanisms contributing to cannibalism at ecdysis, as this behaviour substantially limits culture productivity of several commercially important crustaceans. Before investigating the role of chemoreception in cannibalism of moulting crustaceans, we must investigate its role in detecting moulting conspecifics. Here we use a two-current choice flume to observe juvenile tropical rock lobster (Panulirus ornatus) behavioural response to conspecific moulting cues and identifying attracted and avoidant behaviours correlating to moult stage and social relationship. Observed cue preferences show inter-moult juveniles are attracted to the moulting cues of lobsters to which they are socially naïve. In contrast, post-moult and inter-moult juveniles avoid the moulting cues of individuals whom they are socially familiar with. Average speed and total distance travelled by lobsters increases in response to conspecific moulting cues. This study demonstrates the suitability of a two-current choice flume for behavioural assays in P. ornatus and characterises clear behavioural patterns in juveniles exposed to conspecific moulting cues. This provides important framework for understanding the role of chemical communication in eliciting cannibalism.
Spiny lobsters have a range of complex chemical communication pathways that contribute to feeding behaviour. Feed intake is modulated by feed availability and feed characteristics, such as attractiveness and palatability, with behavioural factors, such as social competition and circadian rhythm, providing an extra layer of complexity. In this study, we investigated the effect of feed frequency on survival and growth of early-stage (instar 2–6) juvenile Palunirus ornatus. In addition, we investigated the interactive effect of feed frequency and circadian rhythm on lobster feed response. Lobsters were fed a set ration at a frequency of either one, two, four, eight, sixteen or thirty-two times per day over 49 days. The effect of feed frequency on growth and survival was determined. Circadian feeding activity under these feeding treatments was assessed by time-lapse photography. Increased feed frequency from one to sixteen feeds daily improved growth by increasing apparent feed intake (AFI) and feed attraction, as confirmed by the increased presence of lobsters in the feeding area. The rapid leaching of feed attractant, particularly free amino acid, suggests a beneficial effect of multiple feeding frequencies on feed intake and growth. However, more than sixteen feeds per day resulted in decreased feed intake and a subsequent reduction in growth. The decrease in feed intake is thought to be associated with saturation of the culture environment with attractants, resulting in a reduced behavioural response to feed supplies. This may indicate the need for depletion of attractants to retrigger a feeding response. As lobsters were grown communally, faster growth at sixteen rations per day was also coupled with increased cannibalism, likely driven by increased vulnerability with the occurrence of more frequent ecdysis events. Whereas circadian rhythm indicated more activity at night, an interaction between daytime activity and feed frequency was not observed.
Biofouling in canals and pipelines used for hydroelectric power generation decreases the flow capacity of conduits. A pipeline rig was designed consisting of test sections of varying substrata (PVC, painted steel) and light levels (transparent, frosted, opaque). Stalk-forming diatoms were abundant in both the frosted and transparent PVC pipes but negligible in the painted steel and opaque PVC pipes. Fungi were slightly more abundant in the painted steel pipe but equally present in all the other pipes while bacterial diversity was similar in all pipes. Photosynthetically functional biofouling (mainly diatoms) was able to develop in near darkness. Different biological fouling compositions generated differing friction factors. The highest friction factor was observed in the transparent pipe (densest diatom fouling), the lowest peak friction for the opaque PVC pipe (lowest fouling biomass), and with the painted steel pipe (high fouling biomass, but composed of fungal and bacterial crusts) being intermediate between the opaque and frosted PVC pipes.
The influence of nucleation on the spectral content of cloud cavitation is investigated using unsteady force measurements and simultaneous high-speed imaging of a rectangular planform NACA-0015 section hydrofoil, with and without upstream nuclei injection. Experiments were conducted for cavitation numbers over the range of 0.60 to 0.45, at a chord-based test Reynolds number of 1.4 × 10 6 , and at an incidence of 6°. The introduction of freestream nuclei was found to significantly alter the cavity topology and spectral content of the force response. Three shedding modes were observed in the case without nuclei injection, while two modes were present with the injection of abundant freestream nuclei. In the nuclei deplete case the dominant shedding frequency is associated with upstream shock propagation and was found to decrease with test cavitation number from a Strouhal number of 0.311 to 0.243, while the sub-harmonic and first harmonic were associated with localized tip and root activity. With the introduction of nuclei the dominant of two distinct shedding frequencies was found to be the lower frequency mode at approximately half that of the corresponding nuclei deplete case, with Strouhal number decreasing from 0.159 to 0.148. The higher frequency mode was shown to be due the propagation of an initial shockwave that only partially condenses the cavity prior to the passage of a second shockwave that leads to full span-wise condensation.
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