Trim control mechanisms such as interceptors and trim flaps have been widely used in recent years in highspeed crafts for ride and trim control. In spite of their extensive application, a few studies investigating the impact of interceptors on planing craft performance, have been published. In the present study, the impact of interceptors on planing crafts hydrodynamic quality is investigated through application of an experimental method. Two scaled-down models of high-speed planing mono-hull and catamaran are tested with and without interceptors in calm water at different heights of the interceptors to investigate the effect of interceptors on drag reduction of the models. The first one is a scaled-down model of 11 m planing mono-hull boat and the test was conducted at the towing tank of Sharif
In this study, a numerical model of unsteady potential flow around submerged marine propellers has been developed. The boundary element approach in combination with time stepping method to model free wake dynamics has been implemented. An important feature of this method in the simulation of pressure-dominant problems is a proper balance between time and accuracy in the numerical process. Another advantage of time stepping method is that there is no need to define wake geometry before modeling. Due to inherent instability of boundary integral equations, a smoothing function to damp the effect of singularities is imposed to the solution. The main innovative idea of this work is that the effect of this mollifier function with different constants for elimination of singularity in mean induced velocity equation has been investigated. The mathematical formulation and implementation of numerical algorithm followed by a number of test cases to verify the model are presented. The results indicate good agreements between model and experiments.
There are various propulsion, maneuvering, and stabilization mechanisms in nature, which can provide inspiration for similar mechanisms in man-made vehicles. This study aims to elucidate and compare the propulsive vortical signature and performance of a foil in two important natural mechanisms of pure pitching and undulatory oscillations. Governing equations are solved with a pressure-based finite volume method solver, in an arbitrary Lagrangian-Eulerian framework domain containing a NACA 0012 foil moving with prescribed kinematics. The results show that in a given Reynolds number (Re), the undulating mechanism produces thrust at a higher Strouhal number (St) and with smaller growth slope, but mostly higher efficiency, versus St, than pitching mechanism. In addition, vortical structures of these mechanisms have significant differences and also vary considerably with St. One of the distinguishable features of vortical signatures is the presence of the leading-edge vortices for the pitching foil, which are not appearing in the undulating foil's vortical pattern.
Fishes, with their efficient propulsive systems and wide variety of body shapes, inspire the design of marine robots. To imitate the kinematics of live species for the fish-like robots, some parameters would be extracted by observations from nature. In this article, a summary is presented over the important literature on the kinematics of the body/caudal swimming of fishes. Then, a detailed procedure to extract the kinematic parameters from live species is discussed. In addition, a procedure is presented to account for the length variations of the vertebral column of the live species during their swimming in the modeling of virtual fishes. Different polynomial and exponential amplitude envelope functions associated with single and multiple sinusoidal terms are also adopted to suggest a better kinematic equation for a body/caudal fin swimmer, spiny dogfish shark (Squalus acanthias). A non-linear least-squares algorithm, Trust-Region, is used to fit surfaces on the experimental data. Results show that in general, the accuracy of the kinematic equation is more affected from the sinusoidal term than the amplitude envelope function. Moreover, evaluations offer the third-and fourth-order polynomial amplitude envelope functions with three sinusoidal terms as appropriate and optimal kinematic equations to model the kinematics of the spiny dogfish shark.
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