How do pistol shrimp make noise

I had a Randall's and the sound reminded me of someone clipping their fingernails. Randomly cut a fingernail or two in the middle of the night and see if your roommate notices.

Mine sounds like clipping toenails. He doesn't snap terribly often. Almost never at night. The pistol and goby will go into their den at night and close it off and go to bed. About the only time mine snaps is if a snail or hermit crab is getting too close to the entrance to the den and he will fire off a couple warning shots. If that doesn't work, he'll just pick them up and move them or bulldoze them out of the way.

You guys are freaking lucky. Mines over a year old and massive. The snaps will wake me up at night easily. Sounds like breaking a wooden dowel.

Well, a small pistol, anyway. I also had a Randall's at one point. I would have to agree with some of the others that it was about as loud as clipping a nail haha. It would not wake me up or anything. Mine was also pretty small about 1 inch. I had a Caribbean Pistol and it was loud. My tank is on the main floor of my house.. I sleep upstairs, door closed, and could clearly hear him at night.

I have a rather large pistol. He can be quite annoying at night when he's probably destroying my snails. I'm quite used to it now so I don't really notice. Oh, I wish he would die Research on cavitation has many practical applications, ranging from fuel injection systems 21 , 22 , ship propellers 23 and pumps 24 , 25 to even drug delivery 26 and cancer treatment Several cases have been examined, for different plunger closure speeds and different plunger sizes.

Here, the focus will be on the results of a case with strong cavitation formation to demonstrate the underlying physical mechanisms. The interested reader is addressed to the supplementary material for a complete reference on all cases.

The developing vortices during the plunger closure are shown in Fig. As the plunger starts to move, flow detachment occurs and two counter-rotating vortices form at the wake of the plunger, indicated with 1.

As the plunger continues to move, these vortices become larger and start to twist, see 2 , 3 and 4. The tip of the plunger is covered by a stretched vortical structure, see 5 , occupied by vapour at its core see also Fig. Later on, vortex instability 33 , 34 , 35 , 36 leads to break-up of the aforementioned structures, see the wake of the plunger at 0. At the same time instant, an attached vortex grows at the wall edge of the socket, due to fluid being expelled from the socket cavity.

Because of the closure speed, a high speed jet is expelled from the opening between the plunger and socket walls. Vortex roll-up is also observed at the sides of the socket walls, due to liquid escaping from the gap between socket walls and plunger, see 7. The same mechanism is in agreement with experimental observations, see 5 , Soon after its formation, the vortex ring elongates, see 9 at 0. Indicative instances of the vortex ring formation, vortical structures indicated using a q-criterion value of 5.

The isosurface is coloured according to local vorticity magnitude, providing an indication of the swirling angular velocity. Note that due to the square opening between plunger and socket, the vortex ring has initially a square shape as well.

Indicative instances of the simplified claw model closure; closure time 0. The formation of the vortex ring is shown in detail in Fig. Initially, at 0.

Note that the rectangular shape of the geometry causes the formation of a rectangular vortex ring as well. Later on, at 0. Its shape still resembles a rectangle, though it is smoothed at corners under the influence of viscosity.

Its shape is elongated in the x -direction, resembling two cylinders with a gap in between, through which the jet moves. The elongated jet shape is caused by the asymmetric flow field promoted by the plunger motion. 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.

They can snap that claw at a speed of about 60 miles per hour. When they do, a giant cavitation bubble, or air bubble, forms.

Then water rushes back into the air bubble, generating powerful energy and providing both a weapon for the shrimp and a loud snapping sound. They study underwater soundscapes, including reef ecosystems.

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