Fig. 3. Schematic drawing of the quasi-steady and unsteady hydrodynamic models. (A) The force generated by a single tail element (E_j) is drawn on the silhouette of the body of a larva from a dorsal perspective. The force generated by this element has components acting towards thrust and laterally. The force generated by the whole tail was calculated instantaneously as the sum of force generated by all tail elements. The position vector of the element (R_j) with respect to the center of mass describes the lever arm used by the tail element to generate a moment about the center of mass. (B,C) Each of the models is illustrated by the vectors that comprise the force generated by the tail element. (B) The force acting on tail elements (E_j) in the quasi-steady model was calculated as the sum of the form force (E_jf) and skin friction (E_js). (C) The force acting on tail elements in the unsteady model was the sum of the quasi-steady forces and the acceleration reaction (E_ja). (D) The coefficient of force acting normal to the surface of a flat plate (C_jnorm) oriented normal to flow. The form force (in green; see equation 21) is found as the difference between the total force (in black; see equation 18) and the force generated by skin friction (in violet; see equation 19). The total force is generated primarily by form force at height-specific Reynolds numbers (Re_jl) of 10³, skin friction is dominant at Re_jl<10⁰, but the normal force is a combination of the two at intermediate Re values.

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