Initial conceptual model for our UV done in April 2014.

First and foremost I apologize for the overall lateness of the content of this post, as I originally intended to publish this post in my previous round of posts, but due to time constraints decided to publish a post on a snake-proof full-body suit (equally interesting!) and invest a little more time into making this post a little easier to understand before publishing…hopefully it worked out, haha.  So as I noted a while back (while discussing the future of undersea warfare), with growing challenges in the undersea and technological domains, innovation is becoming more and more important within the realm of defense engineering (as well as all other fields of engineering).  One promising direction engineers are looking to in all fields of engineering is towards the application of advanced biomimetics (a.k.a. biomimicry) in their designs.  Why might engineers and scientists want to study how we can mimic fish, or other animals or nature in general?  Because nature truly is the ultimate engineer.  Animals have been optimized to perform the tasks that they need to and to do so efficiently and thus have been nearly perfected for their environments and their lifestyles.

Considering the facts just presented, it becomes a little more evident why undersea warfare (as well as other undersea activities and applications) may benefit from the implementation of biomimcry.  Take the Shortfin Mako Shark for example; this is the fastest species of shark in the world and it utilizes its large caudal fin (as will be defined later), slim, streamlined, torpedo-like body, and its stronger, faster-acting muscles (as enabled by its endothermic abilities, through which it generates additional heat through its unique metabolism, keeping the muscles warm and agile, thus defining the Mako as a “warm-bodied shark”) to reach cruise speeds of 25 mph and burst speeds up to 50 mph and leap 30 ft high!  Another example of the awe-inspiring abilities of marine creatures and how scientists and engineers have attempted to mimic them is that of the color- and texture-changing abilities of the octopus, as Andrew talked about a while back.

Shortfin Mako Shark. Photo Credit: Sam Cahir via dmarron.com

To better understand more specifically how engineers can utilize biomimicry in order to advance undersea vehicle technology, we will now discuss how exactly fish swim.  Fish generate forward motion, or swim, through what is termed locomotion.  Locomotion is simply a fancy word for describing movement from one location to another; animal locomotion may take many forms and can be seen in all types of environments, whether terrestial (on land), aerial (through the air), or aquatic (through the water).  There is a myriad of other qualifiers that can be used to further divide up the different kinds of locomotion (if you are interested, you can learn more about animal locomotion at this link), but we are going to solely focus on fish locomotion, that is, how fish get from one place to another.

Fish locomotion can be divided up into two main modes of motion: Body-Caudal Fin (BCF) and Median-Paired Fin (MPF).  The BCF mode accounts for about 85% of fish families’ main mode of propulsion, whereas MPF makes up for about 15%.  Now before diving into the swimming mechanisms associated with these two modes, we will make one more distinction: undulatory motion (also referred to as undulation) vs. oscillatory motion (also referred to as oscillation).  Undulation is by far the most common type of motion (both within the BCF & MPF modes) and can be thought of as a lateral wavelike movement; picture a fish seemingly weaving its way through the water or a rope with waves travelling down its length…this is in essence what undulation manifests itself as: undulation in fish movement appears as lateral waves travelling down the length of the fish’s body.  In short, undulation is lateral wave motion along the length of the body, relative to the body, as if the body was stationary but experiencing waves along its length.  In contrast, oscillation focuses more on the body being essentially rigid and moving the tail side to side…picture your dog wagging its tail, or a pendulum oscillating about the line connecting the pivot point to the base.  Now that we’ve got that covered, we can move on to quickly listing the common types of fish motion and listing a few examples!

Eel anguilliform lateral undulation. Media Credit: lyle.smu.edu

Time-lapse picture showing positions of a dog’s tail throughout its oscillation. Photo Credit: mediaorchard.com

Body-Caudal Fin (BCF)
This type of movement depends on the fish effectively wiggling its body in order to move its caudal fin sided to side, thus producing thrust which has components in the forward, backward, and transverse directions.  The largest component of this thrust is that in the rearward direction, thus the movement of the caudal fin propels the fish through the water.

Undulatory:
1. Anguilliform: With this kind of motion the undulatory waves are passed throughout the entire length of the body (except perhaps the head); because the entire body is extremely flexible, both forward and backward motion are possible.  The most typical application in which you would see this kind of motion would be in eel locomotion.
2. Subcarangiform: This motion is similar to anguilliform, but the forward 1/3-1/2 of the fish does not move, while the rest of the body still generates transverse undulations.  It is now significantly harder for the fish to swim backwards as it is not longer symmetric front to back and the forward portion of the fish is much more stiff than the rear.  Common examples of fish with this kind of motion would be most trout and salmon.
3. Carangiform: Also similar to anguilliform, but only the last 1/3 of the body acts to produce thrust and the caudal fin itself is usually more stiff to produce greater thrust with the reduced active length of the body.  Fish that swim like this are usually fairly narrow transversely, likely to increase the surface area used for thrust generation by increasing the height to width ratio; these fish also tend to be stiffer overall and faster moving.
4. Thunniform: In this group, all undulation is restricted to the caudal fin/tail and the region connecting the main body to the caudal fin (called the peduncle); these types of fish usually have very large, stiff caudal fins, have been optimized for high speeds and long distance travel, and are capable of generating hydrodynamic lift in order to compensate for the fact that many of them are not neutrally buoyant and thus need to move (and in doing so, generate lift) in order to keep from sinking.  Examples are most species of tuna and sharks.

Oscillatory:
1. Ostraciiform: These types utilize slow pendulum-like movement of large caudal fins and are similar to Thunniform, but operate much more slowly.  As a result, this type of swimming is usually either simply an auxiliary, low-energy style of swimming used by some MPF fish or, if used by fish as their main style of propulsion, those fish would generally have internal countermeasures such as poisons since they are incapable of fleeing predators.

Various physical characteristics of a generic shark, nearly all of which appear on most fish.
Photo Credit: Wikipedia.org

Median-Paired Fin (MPF)
This type of movement depends on synchronization of various combinations of usage of the pectoral, dorsal, pelvic, and/or anal fins.

Undulatory:
1. Rajiform: Characterized by vertical undulations along large pectoral fins…think sting rays and manta rays for example.
2. Diodontiform: Characterized by undulations that travel along large pectoral fins…like a porcupine fish!

Porcupine fish with undulating pectoral fins; Diodontiform motion. Media Credit: Tumblr.com

3. Amiiform: Utilize long undulatory waves along large dorsal fins, such as a Seahorse.
4. Gymnotiform: Uses undulations of a long anal fin; much like the Amiiform, but using the anal fin on the underside of the fish rather than the dorsal fin on the top side of the fish.  An example is the American Knifefish.
5. Balistiform: Anal and dorsal fins undulate; while rare, this can be seen in the Triggerfish.

Oscillatory:
1. Tetradontiform: Dorsal and anal fins oscillate either in phase (together) or opposite of each other; an example would be the Sunfish.
2. Labriform: Pectoral fins osciallate in a way in which they produce both lift and drag, which can be resolved into components, one of which would be rewards, thus producing thrust.  In essence, the fish flaps and rows its pectoral fins, producing thrust.  An example of a fish using this kind of motion would be the California Sheephead.

So there you have it, an organized view of the many sorts of propulsion mechanics associated with fish, each having its own advantages and disadvantages.  By studying these kinds of characteristics of fish, scientists and engineers can come up with innovative solutions by looking to the sea for the answers for the one constant truth for scientists and engineers alike is that we never stop learning and so when you can’t find a sufficient answer in your textbooks and theories, you need to be able to conduct experiments and analyze the world around you in order to come up with new ideas.

Personal sketch of a conceptual UV following a submarine in the distance(April 2014).

This is exactly what engineers within the defense industry are doing currently as they conduct research and begin designs of new cutting-edge, innovative undersea vehicles that utilize biomimicry to provide for increased performance, better power efficiency, and increased stealth through the minimization of flow signature.  While we here at Team UV are not utilizing biomimicry in the design of our propulsor (for which we use something else all together), we absolutely have biomimetic influence within our design and as can be seen in the picture at the top of this article, have looked to adapt a streamlined shape and fin-like control surfaces in addition to a number of other biomimetic schemes (i.e. stability, maneuvering, buoyancy control, drag reduction, etc.) to produce a truly innovative solution that is currently in the manufacturing/assembly stage.  And so we again ask for your increased support through our fundraising campaign at GoFundMe.com/TeamUV as we near the end of our project in the coming months.  

As promised, in another week or two, we will release some pictures of the current vehicle design/model.