Octopus-inspired multi-arm robotic swimming

The outstanding locomotor and manipulation characteristics of the octopus have recently inspired the development, by our group, of multi-functional robotic swimmers, featuring both manipulation and locomotion capabilities, which could be of significant engineering interest in underwater applications. During its little-studied arm-swimming behavior, as opposed to the better known jetting via the siphon, the animal appears to generate considerable propulsive thrust and rapid acceleration, predominantly employing movements of its arms. In this work, we capture the fundamental characteristics of the corresponding complex pattern of arm motion by a sculling profile, involving a fast power stroke and a slow recovery stroke. We investigate the propulsive capabilities of a multi-arm robotic system under various swimming gaits, namely patterns of arm coordination, which achieve the generation of forward, as well as backward, propulsion and turning. A lumped-element model of the robotic swimmer, which considers arm compliance and the interaction with the aquatic environment, was used to study the characteristics of these gaits, the effect of various kinematic parameters on propulsion, and the generation of complex trajectories. This investigation focuses on relatively high-stiffness arms. Experiments employing a compliant-body robotic prototype swimmer with eight compliant arms, all made of polyurethane, inside a water tank, successfully demonstrated this novel mode of underwater propulsion. Speeds of up to 0.26 body lengths per second (approximately 100 mm s(-1)), and propulsive forces of up to 3.5 N were achieved, with a non-dimensional cost of transport of 1.42 with all eight arms and of 0.9 with only two active arms. The experiments confirmed the computational results and verified the multi-arm maneuverability and simultaneous object grasping capability of such systems

Optimal Strouhal number for swimming animals

To evaluate the swimming performances of aquatic animals, an important dimensionless quantity is the Strouhal number, St = fA/U, with f the tail-beat frequency, A the peak-to-peak tail amplitude, and U the swimming velocity. Experiments with flapping foils have exhibited maximum propulsive efficiency in the interval 0.25 < St < 0.35 and it has been argued that animals likely evolved to swim in the same narrow interval. Using Lighthill's elongated-body theory to address undulatory propulsion, it is demonstrated here that the optimal Strouhal number increases from 0.15 to 0.8 for animals spanning from the largest cetaceans to the smallest tadpoles. To assess the validity of this model, the swimming kinematics of 53 different species of aquatic animals have been compiled from the literature and it shows that their Strouhal numbers are consistently near the predicted optimum.Comment: 21 pages, 6 figure

Who fits in? : What social markers are important for acculturation in Finland

Immigration to Finland has seen a significant rise since the 1990s. The adaptation of immigrants to the society is a relevant and popular theme in public discussion. This study explores the opportunities of immigrants to adapt to and become members of the Finnish society, as reported by Finnish respondents. Acculturation is an extensively studied field, but it has rarely been studied through social markers of the receiving society, or through the opinions and attitudes of the native majority population. In this study, a new angle is introduced through the analysis of acculturation opportunities for immigrants from the perspective of the native Finnish. The study was carried out with a quantitative method. The SPSS tool was used for handling data. The data material has been gathered with a questionnaire sent to students at the University of Helsinki and at Aalto University (N=198). The outline of the questionnaire is borrowed from that of a larger research project, where Singapore, Canada and Japan are studied in addition to Finland. The central research questions are: first, who fits in, secondly, is it possible to fit in, and thirdly, what factors predict why some people are more reluctant than others to accept immigrants as parts of the ingroup. The theoretical background of the study is based on John W. Berry’s acculturation studies. The theoretical models used are the Interactive Acculturation Model (IAM) and the Relative Acculturation Extended Model (RAEM), which have been derived and elaborated from Berry’s work by other researchers. In order to support the analysis and discussion of results, a number of hypothetical models have been used, such as G.W. Allport’s contact hypothesis, the similarity attraction hypothesis and the culture distance theory. The results were analyzed through the creation of three dimensions of acculturation, i.e. sociocultural adaptation, socioeconomic adaptation, and social psychological adaptation. The results indicate that Finns set greatest expectations for acculturation in the social psychological dimension, followed by the sociocultural dimension and lastly by the socioeconomic dimension. For the most part, Finns are confident that immigrants can achieve these expectations with relative ease regardless of the dimension of acculturation. In addition, the study found that certain factors, such as greater perceived threats, explained greater expectations of acculturation.Maahanmuutto Suomeen on lisääntynyt huomattavasti 1990-luvun alusta lähtien. Maahanmuuttajan sopeutuminen suomalaiseen yhteiskuntaan ja kulttuuriin on tullut ajankohtaiseksi puheenaiheeksi. Tässä tutkimuksessa tarkastellaankin juuri maahanmuuttajan sopeutumismahdollisuuksia eli akkulturaatiota suomalaiseen kulttuuriin. Akkulturaatio on paljon tutkittu ilmiö, mutta sitä on harvoin tutkittu vastaanottavan yhteiskunnan sosiaalisten erityispiirteiden ja enemmistön mielipiteiden ja asenteiden kautta. Tämä tutkimus tarjoaa uutta ulottuvuutta akkulturaatioon keskittymällä sosiaalisten erityispiirteiden (engl. social markers) merkitykseen sopeutumisessa. Tutkimuksessa analysoidaan maahanmuuttajien akkulturaation mahdollisuuksia suomalaissyntyisten Suomen kansalaisten näkökulmasta. Tutkimus on toteutettu kvantitatiivisesti. Työkaluna aineiston käsittelyssä on käytetty SPSS-tilasto-ohjelmaa. Tutkimuksen aineisto on kerätty kyselylomakkeella Helsingin yliopiston ja Aalto-yliopiston opiskelijoilta (N = 198). Kyselylomake pohjautuu laajempaan tutkimushankkeeseen, jossa tutkitaan Suomen lisäksi mukana Singaporea, Kanadaa ja Japania. Tämä tutkimus on osa kyseistä laajempaa tutkimushanketta kuitenkin vain kyselylomakkeen ja aihe-alueen osalta. Keskeisimmät tutkimuskysymykset ovat seuraavat: ensinnäkin, kuka sopii joukkoon, ja toiseksi, onko joukkoon mahdollista sopia sekä kolmanneksi, mitkä tekijät ennustavat, miksi toiset ovat tiukempia kuin toiset hyväksyäkseen maahanmuuttajan osaksi sisäryhmää. Tutkimuksen teoreettinen tausta rakentuu John W. Berryn akkulturaatiotutkimuksille. Tässä tutkimuksessa teoreettinen lähtökohta ovat Berryn akkulturaatiomallista johdettu Interactive Acculturation Model (IAM) ja Relative Acculturation Extended Model (RAEM). Tulosten analysoinnissa on käytetty lisäksi erilaisia hypoteettisia malleja, esimerkiksi Allportin (1954) kontaktihypoteesia, samanlaisuus-attraktio-hypoteesia ja kulttuurisen distanssin teoriaa tukemaan keskustelua tuloksista. Tulokset muodostuivat kolmesta kokonaisuudesta, joita ovat sosiokulttuurinen sopeutuminen, sosioekonominen sopeutuminen ja sosiaalipsykologinen sopeutuminen. Tulokset osoittavat suomalaisten vaativan maahanmuuttajilta eniten sosiaalipsykologisen sopeutumisen saralla, toiseksi eniten sosiokulttuurisen ja vähiten sosioekonomisen sopeutumisen saralla. Enimmäkseen suomalaiset uskovat maahanmuuttajan voivan helposti saavuttaa heidän asettamansa ehdot jokaiseen eritasoiseen sopeutumiseen. Lisäksi, tulokset osoittavat, että juuri tietynlaiset tekijät, kuten esimerkiksi koettu uhka, ovat yhteydessä korkeampiin akkulturaatio odotuksiin

A new type of biomimetic fish with oscillatory propulsion method

The traditional multi joint mechanical serial parallel structure biomimetic fish has lower propulsive efficiency, more energy transmission loss, more complicated mechanical design and control algorithms because of more mechanical joints. While the flexible body has infinite degrees of freedom, and the energy in it is stored by elasticity and inertia, it is more viscous than that of multi joints. This project studies the principle of carangidae fish in carangidae carp, takes it as the bionic object, and designs a biomimetic fish with a flexible body tail structure to improve propulsive efficiency. This study explores the biomimetic fish propulsion speed and caudal aspect ratio, caudal oscillation frequency, modal distribution curve, and optimizes a parameter set of fish tail that can achieve effective promotion. So it is good for the exploration of the development of high speed, high efficiency, high maneuverability of bionic propeller swing on theoretical basis and practical aspects

Hydropower development, riverine connectivity and non-sport fish species: Criteria for hydraulic design of fishways

Hydropower barriers are among the most conspicuous anthropogenic alterations to natural riverine connectivity, resulting in species-specific effects linked to dispersal abilities, especially swimming performance. They may present a particular problem for small-bodied ‘non-sport fish’, such as those that characterize the freshwater communities of temperate regions in the Southern Hemisphere. Recent studies have suggested that nature-like fishways could ensure passage of diverse fish assemblages through hydropower barriers. Through experiments performed in a swim tunnel, we present, for the first time, fishway design criteria for two non-sport species endemic to Chile, a country experiencing rapid hydropower development. Incremental velocity tests showed that Cheirodon galusdae and juveniles of Basilichthys microlepidotus were capable of very similar standardized critical swimming speeds of 69.7 and 69.6 cm s-1 respectively. When expressed in units of body lengths, C. galusdae was capable of very high critical speeds of 16.2 bl s -1, whereas for B. microlepidotus this was 7.6 bl s-1. However, fixed velocity tests revealed that the swimming endurance of the latter species was slightly higher. Dimensionless analysis showed a clear relationship between fatigue time and fish Froude number, similar to that already described for subcarangiforms. Based on these results we present fishway design curves indicating a transition from sustained to prolonged swimming at a fishway length of 15 m. Our results show that the swimming capacity of these species is well-suited to the mean flow velocity field described for nature-like fishways. However, more work is required to understand the effects of turbulence on the passage of non-sport species

Emerged Coupling of Motor Control and Morphological Development in Evolution of Multi-cellular Animats

A model for co-evolving behavior control and morphological development is presented in this paper. The development of the morphology starts with a single cell that is able to divide or die, which is controlled by a gene regulatory network. The cells are connected by springs and form the morphology of the grown individuals. The movements of animats are resulted from the shrinking and relaxation of the springs connecting the lateral cells on the body morphology. The gene regulatory network, together with the frequency and phase shifts of the spring movements are evolved to maximize the distance that the animats can swim in a given time interval. To facilitate the evolution of swimming animats, a term that awards an elongated morphology is also included in the fitness function. We show that animats with different body-plans emerge in the evolutionary runs and that the evolved movement control strategy is coupled with the body plan