Browsing by Author "Hoerner, Stefan"

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    On the influence of head motion on the swimming kinematics of robotic fish
    (2022) Abbaszadeh, Shokoofeh; Kiiski, Yanneck; Leidhold, Roberto; Hoerner, Stefan;
    Up to now bio-inspired fish-mimicking robots fail when competing with the swimming performance of real fish. While tail motion has been studied extensively, the influence of the head motion is still not fully understood and its active control is challenging. In this experimental study, we show that head yawing strongly impacts on the propulsion force and determines the optimal fin actuation amplitude and tail beat frequency when aiming for a maximal propulsion force. In a parametric experimental study on a tethered 367 mm long fish robot the pivot point location of the head yaw has been varied along with tail beat frequency and actuation amplitude. The experiments took place in a still water tank and the swimming force has been measured with a single axis load cell. The robot is actuated with non-conventional area actuators based on micro fiber composites. 105 parameter sets have been investigated while the highest pivot point distance of roughly 0.36 body length from the nose tip provided the highest propulsion force of 500~mN with the lowest actuation frequency of 2.5 Hz and the highest head motion amplitude of a magnitude of 0.18 body length. Even though the pivot point location on a free swimming robot is a consequence of the complex fluid-structure interactions of fish and fluid, the results provide valuable information for the design of fish mimicking robots and questions the paradigm that head yaw is a simple recoil effect from tail motion and has to be minimized for an effective propulsion.
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    Supplementary data to: An open numerical model for the investigation of flow environments as experienced by freshwater fish
    (Otto-von-Guericke-Universität Magdeburg, 2022) Khan, Ali Hassan; Ruiz Hussmann, Karla; Powalla, Dennis; Hoerner, Stefan; Kruusmaaa, Maarja; Tuhtan, Jeffrey A.
    This data set comprises the supplementary materials of a benchmark case of the flow around a fish shaped body for numerical ecohydraulic and biological studies including a validated numerical model. The set comprises both experimental and numerical data. Flow measurements of a 3D printed fish shaped body were conducted with a 2D LDA device. The data set also includes a computational fluid dynamics model validated against the LDA data. The numerical model is based on the open source software tool OpenFOAM. All settings for experiments and the simulation case file are included for further research.