Ocean Engineering 148 (2018) 75–114 Contents lists available at ScienceDirect Ocean Engineering journal homepage: www.elsevier.com/locate/oceaneng Review Classification of biological and bioinspired aquatic systems: A review R. Salazar, V. Fuentes, A. Abdelkefi * Department of Mechanical and Aerospace Engineering, New Mexico State University, Las Cruces, NM, 88003, USA ARTICLE INFO ABSTRACT Keywords: Robotic systems capable of aquatic movement has increased exploitation in recent years due to the diverse range Aquatic systems of missions that can be performed in otherwise hostile environments. These aquatic unmanned vehicles (AUVs) Bioinspiration have begun to transition to systems that replicate biological animals as they are already extremely efficient at Fin oscillation moving in aqueous environments. The result is the abandonment of inefficient propeller based locomotion for a Fin undulation biological locomotion type suitable for the specific mission. There is a diverse range of biological locomotion's Jet propulsion available with animals that give a range of criteria to follow. In this review, existing aquatic animals and found AUVs are classified. How the bioinspired systems compare to the animals in their locomotion is investigated and discussed. Then, it is discussed what makes these systems bioinspired and biomimetic, and the AUVs that fall into these distinctive categories. Limitations and future recommendations on possible improvements for these systems are offered. 1. Introduction missions include environmental surveying, oil spill monitoring, internal pipe inspection, erosion monitoring, observation of animal species, Currently, there is a growing need for the adaptation of robotic sys- beach safety, espionage, anti-espionage, and border patrol (Blindberg, tems which can autonomously perform routine tasks in aquatic envi- 2001; Najem et al., 2012). The mission of an AUV is dependent on its ronments (Blindberg, 2001; Habib, 2013; Scaradozzi et al., 2017; Raj and design. However, a major component of the AUV is the autonomy of the Thakur, 2016; Yen and Azwadi, 2015). This need derives from the large system. An autonomous system is necessary for the completion of these scale unobservable volume of the oceans and other bodies of water which missions because signal transmission through water is difficult, espe- all present a challenge for hominoid observation. This challenge persists cially at great depths or distance. The craft needs to carry out pre- due to human fragility in aqueous environments and the underdeveloped planned mission solely on its own and should respond to changing robotic systems that are deployed. To solve the lack of mission capabil- environment. In addition, these systems need to have long endurance ities of these systems, inspiration must be taken from the diverse selec- and have the capability to move in close quarter environments with tion of species which inhabit the oceans, rivers, and lakes. Deriving constantly changing fluid flow. A close quarter environment would not inspiration from nature would mean the system is bioinspired. If the condone a system tethered with a control cable or that of those using system mimics a biological system, it is dubbed biomimicry. There have propellers. Propeller thrust degrades when fluid flow is not uniform. already been studies where researchers used bioinspiration and bio- Propellers are also inefficient in comparison with fishes where pro- mimicry to make an autonomous vehicle. These new robots are charac- pellers are estimated efficiency of 40–50 percent (Habib, 2013). Fishes terized as an aquatic unmanned vehicle (AUV). These AUVs are modeled have the ability of changing direction at a complete stop which is highly after certain fish species which the investigators deemed to be the best beneficial in close quarter environments. For example, systems com- form to replicate. This review offers a thorough classification list for parable with the Eel would be useful in pipe inspection where large biological and AUV systems. In this effort, more current and dated sys- body contortion is necessary to navigate complex bends. Furthermore, tems are compiled into one location to allow for future investigators Tuna are extremely efficient swimmers. Such, a robot that has a high searching AUV system reference information. More available information level of biomimicry could also display high speed required for specific allow the opportunity to create optimized AUVs. (see Table 26) missions. Depending on mission requirements, a biological system AUVs would have application in a wide range of civilian and mili- should be the center point for the design because of their swimming tary missions for exploitation in marine or aquatic environments. These capabilities. * Corresponding author. E-mail address: [email protected] (A. Abdelkefi). https://doi.org/10.1016/j.oceaneng.2017.11.012 Received 14 September 2017; Accepted 5 November 2017 0029-8018/© 2017 Elsevier Ltd. All rights reserved. R. Salazar et al. Ocean Engineering 148 (2018) 75–114 The current unmanned submersible systems being used in civilian et al., 1999; Colgate and Lynch, 2004; Lauder, 2015; Neveln et al., 2013) and military missions are all relatively similar where by systems use allow for a starting point where ideas can be gathered and amassed into propellers for thrust. These unmanned submersibles have been adapted one place. The reviews of AUVs lack certain topics or overview of sys- from their larger manned relatives when the utility and safety of these tems. This review fills voids in this research and offers it in a clearer systems was realized (Blindberg, 2001). Autonomous aquatic robotic format. The review is organized as follows: in Section 2 the biological systems have been used with rapid growth of use since the 1970s locomotion and species are outlined. In Section 3, the found AUVs are (Blindberg, 2001). However, the most substantial exploitation increase is described and organized. In Section 4, there is an in-depth discussion from 1990 to 2010 with the first commercial products coming about in about the best AUVs, compare them to the biological, and the most the 2000–2010 timeframe (Blindberg, 2001). These systems are often critique for biomimicry systems. In Section 5, summary conclusions outfitted with observation equipment like cameras, temperature gauges, are presented. salinity instruments, and acoustic mapping (Blindberg, 2001; Cruz et al., 1999). These systems can be separated into two classifications. There are 2. Biological locomotion and species the torpedo-shaped autonomous systems which have been widely used on more long endurance and faster speed missions. These types of sys- There are several methodologies that can be used to define the tems have been extensively used because of their long range and depth locomotion characteristics. This review proposes a more encompassing capabilities (Blindberg, 2001). Systems like those used to track migratory and straightforward classification for the biological systems that can be shark species by acoustic tag tracking have been implemented with applied to the found AUVs. Locomotion is divided into three main clas- mixed results (lost connection with signal beacon) (Lin et al., 2013). sifications, namely, Fin Oscillation, Fin Undulation, and Jet Propulsion. Scientist tag a shark with an acoustic tag and then a torpedo-shaped AUV This is the first review that combines these locomotions. There are many follows this beacon at a predetermined distance (Lin et al., 2013). This categories within these main classes, along with overlap between them. allows for the observation of depth, temperature of water, salinity, along The classification and categories are presented in Fig. 1. The Fin Oscil- with GPS location of the animal (Lin et al., 2013). There are lation has one of the largest categories, the well-known caudal fin torpedo-shaped robots capable of long range missions, known as gliders swimmers. While the largest class in Fin Undulation is pectoral fin were swept up by the military (Guizzo, 2008). These glider submersibles swimmers. The Jet Propulsion class is amongst the smallest defined, there work on an efficient and clever system that uses buoyancy and winged is not as much variety in this class. The Dorsal & Anal Fin Oscillation is flight to accomplish forward movement (no propellers) (Guizzo, 2008). described in the Fin Oscillation section. The Oscillation & Undulation is By filling and emptying ballast tanks, the craft is capable of changing detailed in the Fin Undulation. Moreover, the combination Jet & Fin depth. During depth change large control surfaces give the craft forward Undulation is described in Jet Propulsion. direction. Other types of submersible robots are the slower and less hy- The terminology for the Fin Oscillation was taken from Sfakiotakis drodynamic robots that are comparable with the Kambara (Wettergreen et al. (1999). where a detailed review is given for different types of fish et al., 1998). These systems are used often because of their appendage locomotion. Some of the same terminology is needed for the explanation attachments and their adequate close-proximity control. These systems of the AUV systems. Thus, this terminology is given to allow a better are often simple where an open frame external cage contains all the understanding of types of fins and what nomenclature are used in the equipment, and not much focus is placed on their efficiency (Wettergreen various categories of locomotion. Shown in Fig. 2(a) and (c), respec- et al.,