How does pistol shrimp

The jet is extremely powerful and causes the formation of a cavitation ring. The likely physics of this are described very well in this article. When the mechanism is activated, there is a very loud popping or crackling sound. Imagine how loud the sound would be if the shrimp were much larger! By the way, both pistol shrimps and mantis shrimps create cavitation bubbles that are so powerful that they reach temperatures almost as high as those on the surface of the sun, resulting in a glow sonoluminescence.

But the glow is too faint and fast for us to see without the help of special instrumentation. Pistol shrimp use their power defensively, and possibly also in competition. What would human-sized pistol shrimp powers actually look like?

Does the movie seem off or on-target about it? If human-sized, the pistol mechanism would still work, but it might be hard to make it proportionately as powerful because at the larger scale a great deal more force would be required to have the same effect.

The problem is similar to that of movies about immense insects. They would either look very different than they do as teensy guys, or they would simply collapse under the weight of their exoskeletons. Is the pistol shrimp secretly the most powerful animal by scale? Well, first of all, its power is no secret to those in the know!

The normal background sound is a loud din of crackling and popping — the social life and strife of all the pistol shrimp in the vicinity playing out for you in surround-sound! As for power, there are many herculean lilliputians. Of course we all know about the seemingly disproportionate strength of ants and other small arthropods. So really, because of the way scaling works, just being tiny makes amazing things happen.

Think of it like being born on the planet Krypton and then traveling to Earth. Foxx is tired, basically dead, after doing his form of supercavitation. It's a friendship that at any moment could be undone by the shrimp accidentally snapping the goby in the face and knocking it unconscious.

Not unlike most friendships, really. Another species will dig a sandy burrow and invite a goby over. The lovely new couple will hover at the entrance on the lookout for both prey and predator.

So if the goby runs back into the burrow, the shrimp withdraws as well. But most incredible of all symbiotic snapping shrimp relationships are the handful of species that actually form societies of hundreds of individuals inside sponges, an extremely advanced level of organization known as eusociality. The shrimp are ruled by a larger queen and king, the only ones who breed, surrounded by their doting subjects.

Those hairs allow the pistol shrimp to detect the snaps of its fellow species. Indeed, disputes involve two shrimp standing just far enough away from each other so they can blast back and forth without blowing each other's heads off. We humans would call this posturing. The shrimp would call it snap. Snap is really all they know. These species are exceedingly tiny, about the size of a grain of rice. They consume whatever falls into the sponge and scrape tissue off of their host as well.

It is very tempting to wonder if we can utilize the heat created by such cavitation processes as an energy source. One idea might be to create a mechanical replica version of the pistol shrimp.

Its not clear whether such energy production, even if driven by hydro or heat harvesting, would be more efficient than other methods of energy production.

Also what might be more difficult is maintaining the integrity of the vacuum bubble for anything more than a tiny size. The tiny size of bubbles could however perhaps be an advantage in other applications. The small bubbles could be useful medicine for tumor destruction for example [3].

Another idea that has been floated has been a compression engine [4]. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for non-commercial purposes only.

Finally, at 0. Colouring in Fig. Under the assumption of forced or rigid body vortex type, vorticity and angular velocity are linked. Vorticity is twice the angular velocity of the instantaneous principal axes of the strain-rate tensor of a fluid element The induced liquid depressurization defined as pressure at vortex radius R , p R , minus the pressure at the vortex core, p c may be expressed as 13 :. This value is similar to the one used as a fitting parameter by Versluis et al.

It should be noted that the forced vortex assumption is not necessarily far from reality, since real fluid vortices are combinations of forced and free vortices.

Moreover, this assumption serves to provide an order of magnitude estimate of the angular velocity, explaining the induced liquid depressurization. In Fig. This combined representation enables to link cavitation structures with vortical structures. At the start of the plunger motion, attached cavitation develops at the wake of the plunger due to local flow detachment.

As the plunger accelerates, reaching maximum angular velocity, flow detachment at the sides and the tip of the plunger induces the formation of cavitation sheets, see 1 at 0. Later on, detached cavitation structures are observed at the plunger wake at the cores of vortices, e. The rapid plunger closure leads to the formation of a cavitating vortex ring around the high speed jet, which is clearly shown in 4.

After formation, the cavitation vortex ring moves following the jet and oscillates, collapsing and then rebounding again, see the sequence of 5 - collapse , 6 - minimum size and 7 - rebound. At the same time, the strong flow acceleration, due to vortex rebound deforms the vortex even more and shatters the cavitation ring. To demonstrate with clarity the flow field, Fig.

The core of the vortex ring is tracked over time and annotated with arrows. Instances in Fig. Interaction of the jet with fluid from the plunger wake leads to a deviation of jet and cavitation vortex ring from the horizontal direction. Indeed, the jet-wake interaction imparts downward momentum to the jet, which is observable in the presented instances in Fig. Similar effect was observed in the experiment as well and it is demonstrated in the validation study in the supplementary material.

Even though cavitation ring rebounding might seem unexpected, the rebound mechanism is physical and is related to conservation of angular momentum. Indeed, it may be proven that, for a vortex cylindrical or toroidal , circulation acts in a similar way to a non-linear spring, preventing complete collapse, since the induced centrifugal forces tend to increase the vortex size, eventually leading to rebound, see J. Franc In essence, as long as vorticity is preserved e. The collapse time for a toroidal cavitation ring may be approximated as 13 :.

Since in nature pistol shrimps are not identical, it is reasonable to expect variations in the claw size or closure speed. For this reason, a parametric investigation was performed to determine the effect of the closure speed to jet velocity and cavitation volume. Jet velocity is measured at the neck of the formed orifice, as in the experiment 5. The peak jet velocity is a linear function of the maximum plunger closure velocity see Fig. In all cases a local minimum is found after the jet velocity peak, which is closely followed by a second peak, much smaller than the first.

This second peak is associated with flow reversal inside the socket. Indicative instances of the flow reversal are shown in supplementary material.

Figure 7 shows the vapour volume in the cavitation ring formed by the plunger closure in respect to time. A global maximum of vapour volume is clearly observed around the time of plunger closure, closely followed by a local minimum due to the cavitation ring rebound. Discrepancy is expected, mainly because equation 2 is applicable for small minor to major torus radius ratio and a perfectly circular ring, which is obviously not the case here.

Calculation performed as the volume integral of the vapour volume fraction. This form resembles the dynamic pressure contribution 0. As already demonstrated, the plunger speed is linearly related to the jet speed. The jet speed affects the pressure inside the vortex core, since vortex pressure is a quadratic function of tangential vortex velocity It is highlighted that Fig. In any case, for the sake of completeness, it is mentioned that the trend relating maximum vapour volume in the whole computational domain to the closure speed is similar to the one shown in Fig.

As the cavitation ring collapses and rebounds, very high pressures are produced due to sharp deceleration of surrounding liquid.

In essence, the sudden deceleration of liquid results to a water-hammer effect, consequently emitting a pressure pulse. This pressure pulse is the speculated mechanism employed by the pistol shrimp to stun or kill its prey The generated pressure peak is closely related to the amount of vapour produced during the plunger closure. When the plunger moves at the highest speed examined here closure at 0. Pressure peak due to cavity collapse, plunger closure at 0. Pressure is shown at a midplane slice.

Before the time of 0. Then, from 0. The pressure peak is then followed by a second pressure drop. The pressure signal pattern is the same as the one found in the prior work by Versluis To summarize, the present work is the first to analyze the cavitating flow in a geometry resembling a pistol shrimp claw, providing insight in the physical mechanisms of cavitation generation and proving that cavitation produced by the shrimp claw is not a spherical bubble but rather a toroidal cavitation structure.

The main mechanism of the cavitating claw operation is vortex ring roll-up, induced by the high speed jet expelled from the socket. Depending on the plunger closure speed, circulation of the vortex ring may become high enough to cause a considerable pressure drop inside the vortex core.

A large pressure drop may induce vaporization of the liquid inside the vortex core, leading to the formation of a cavitating vortex ring. Upon its formation, the cavitation ring travels at the direction of the jet, with a translational velocity around half of that of the jet and its minor radius oscillating until viscosity dissipates angular momentum. The oscillation of the cavitation ring leads to periodic collapses and rebounds, which emit high pressure pulses.

Considering all the aforementioned observations, similarities and differences of the flow produced by a simplified and an actual pistol shrimp claw may be summarised.

First of all, from the results it is clear that, as the claw plunger moves inside the socket, the displaced liquid forms a high velocity jet, which in turn induces vortex ring roll-up. The shape of the vortex ring will affect the shape of cavitation in the vortex core.

In the simulation, cavitation at the wake of the plunger was observed. In reality, the streamlined shape of the claw means that flow detachment is limited, thus there is very little cavitation, if any. Moreover, whereas in simulation the socket was fixed in place, in actual pistol shrimp claws both plunger and socket move at opposite directions, offsetting somewhat the jet deviation introduced by the plunger wake.

Despite these differences, quantitative characteristics of claw operation have been reproduced. The pressure drop predicted by the intense swirling motion of the liquid is very similar to the one imposed as fitting parameter by Versluis et al.

Moreover, the peak pressure measured from the bubble collapse is comparable to the one found from the present study, see P. Krehl 1 , and the pressure signature is very similar to that measured by Versluis et al. It is also highlighted here, that effects found in the simulations may be confirmed by early investigations of other researchers, working on similar simplified claw models under cavitating conditions, see the work of Eliasson et al.

The numerical methodology used in the present work is discussed in detail in the supplementary material, but will be described here briefly. The plunger motion is imposed using an Immersed Boundary IB technique 41 , 42 , The advantage of this technique is that the computational domain remains unchanged throughout the whole simulation time, thus greatly simplifying geometry manipulation, especially in cases of small gaps or contact regions.

Cavitation is modelled using the Homogenous Equilibrium Assumption 15 , 44 , 45 , 46 , thus pressure and density are directly linked through an Equation of State EoS describing the phase change process. This assumption is justified based on cavitation tunnel experiments The geometry used for the simulations is based on prior experimental studies 5.

Experiments were based on the claw morphology of a typical specimen of snapping shrimp, A. A two dimensional slice was extracted along the midplane of the claw geometry, obtaining the mean profile of plunger and socket geometry. This two dimensional slice was extruded in the 3rd direction, to obtain a simplified model of the shrimp claw. Additionally, scale similarity was exploited to manufacture an enlarged scale model of the claw scale , which has been used for experimental studies, involving flow visualization and Particle Image Velocimetry.

In the scope of the present study, two types of simulations have been performed. The aim of this simulation was to validate the numerical framework and detailed results are presented in the supplementary material. Results of the second set of simulations are presented in this paper, since they involve cavitation related effects which are the focus of the study. As shown in Fig. Such features are not necessary for the simulation, since the area of interest is in the flow channel between plunger and socket.

Thus, such features have been removed Fig. Moreover, the fillet of the geometry has been removed Fig.