No abstract

Designing a robotic fish is a challenging endeavor due to the non-linear dynamics of underwater environments. In this paper, we present an evolutionary computation approach for designing the caudal fin of a carangiform robotic fish. Evolutionary experiments are performed in a simulated environment utilizing a mathematical model to approximate the hydrodynamic motion of a flexible caudal fin. With this model, time-consuming computational fluid dynamic simulations can be avoided while maintaining a physically realistic simulation. Two approaches are employed to maximize a robotic fish's average velocity. First, a hill-climbing algorithm is applied to find the optimal stiffness for a fixed shape caudal fin. Next, both fin stiffness and shape are simultaneously optimized with a genetic algorithm. Additionally, simulated caudal fins are compared to physically validated fins, which were fabricated with the aid of a 3D printer and tested on a robotic fish prototype. Results show a correlation between evolved results, model predicted behavior, and physical robot performance with some disparity due to the difficulty in accurately approximating real world performance in a simulation environment. Despite the disparity, evolutionary design is shown to be a viable process.

I describe the approach followed by the Ancient Monuments Laboratory in adapting the instrumentation and techniques of resistivity and magnetic prospecting to the near‐surface problems of mapping buried archaeological sites. Such sites demand rapid and intensive ground coverage and the highest possible spatial resolution and instrument sensitivity. Resistivity is used largely for planning building foundations. Optimized resistivity results have required comparative studies of electrode configurations and the effect on resistivity of climatic variations in different lithologies. Magnetic prospecting is especially effective for detecting (1) fired structures such as kilns, and (2) excavated features such as ditches and pits filled with topsoil of relatively high susceptibility (which is further enhanced by human activities). Speed and resolution requirements have caused the proton magnetometer to be abandoned in favor of the fluxgate gradiometer. Valuable information about human activity can also be obtained from magnetic susceptibility measurements on topsoil.

SummaryNo accurate survey of a flint mine exists. It is planned to carry out such a survey at Grime's Graves over a period of several years. Its purpose is to study the growth of the flint-mine complex, the evaluation of mining techniques and ancillary industries, and trade relations; and to discover settlement sites related to the industrial complex. Preliminary field work was carried out in the summer of 1972. This included geophysical and chemical surveys, ground surveys, and aerial photography. Excavations were undertaken to test the results of the scientific surveys. A detailed contour map of the site was prepared by photogrammetry.

Robotic fish accomplish swimming by deforming their bodies or other fin-like appendages. As an emerging class of embedded computing system, robotic fish are anticipated to play an important role in environmental monitoring, inspection of underwater structures, tracking of hazardous wastes and oil spills, and the study of live fish behaviors. While integration of flexible materials (into the fins and/or body) holds the promise of improved swimming performance (in terms of both speed and maneuverability) for these robots, such components also introduce significant design challenges due to the complex material mechanics and hydrodynamic interactions. The problem is further exacerbated by the need for the robots to meet multiple objectives (e.g., both speed and energy efficiency). In this paper, we propose an evolutionary multiobjective optimization approach to the design and control of a robotic fish with a flexible caudal fin. Specifically, we use the NSGA-II algorithm to investigate morphological and control parameter values that optimize swimming speed and power usage. Several evolved fin designs are validated experimentally with a small robotic fish, where fins of different stiffness values and sizes are printed with a multi-material 3D printer. Experimental results confirm the effectiveness of the proposed design approach in balancing the two competing objectives.