A finite element method for non-linear hyperelasticity applied for the simulation of octopus ARM motions

An implicit non-linear finite element (FE) numerical procedure for the simulation of biological muscular tissues is presented. The method has been developed for studying the motion of muscular hydrostats, such as squid and octopus arms and its general framework is applicable to other muscular tissues. The FE framework considered is suitable for the dynamic numerical simulations of three-dimensional non-linear nearly incompressible hyperelastic materials that undergo large displacements and deformations. Human and animal muscles, consisting of fibers and connective tissues, belong to this class of materials. The stress distribution inside the muscular FE model is considered as the superposition of stresses along the muscular fibers and the connective tissues. The stresses along the fibers are modeled as the sum of active and passive stresses, according to the muscular model of Van Leeuwen and Kier (1997) Philos. Trans. R. Soc. London, 352: 551-571. Passive stress distribution is an experimentally-defined function of fibers’ deformation; while active stress distribution is the product of an activation level time function, a force-stretch function and a force-stretch ratio function. The mechanical behavior of the surrounding tissues is determined adopting a Mooney-Rivlin constitutive model. The incompressibility criterion is met by enforcing large bulk modulus and by introducing modified deformation measures. Due to the non-linear nature of the problem, approximate determination of the Jacobian matrix is performed, in order to utilize the full Newton-Raphson iterative procedure within each time-step. In addition, time discretization is performed via the implicit Newmark method. We developed an open-source finite element code that is capable of simulating large deflection maneuvers of muscular hydrostats. The proposed methodology is validated by comparing the numerical results with existing measurements for the squid arm extension. The efficiency and robustness of the proposed numerical method is demonstrated through a series of octopus arm maneuvers, such as extension, compression and bending

Propulsive efficiency in drag-based locomotion of a reduced-size swimmer with various types of appendages

The propulsive efficiencies of multi-functional appendage configurations in a small drag-based swimmer are investigated computationally. Due to the lack of actual actuators to measure input power, efficiency is evaluated indirectly and may be instinctively associated to higher production of forward thrust. However, the relation is not intuitively self-evident, since the shape of the propulsive system is known to influence the generation of hydrodynamic forces, along with the particular kinematics used, which in turn affect the power consumption. The current article investigates this topic in the case of a reduced-size appendage-based swimmer producing small values of thrust, and discusses the role of design in the relation between propulsive efficiency and thrust production under a ``sculling" kinematic motion profile. The study implements seven different shapes of appendages, inspired by both the biology and engineering, which perform a drag-based swimming pattern while being attached, in pairs, at the dorsal side of a common body. The work utilises an immersed boundary approach to solve numerically the fluid equations and capture the flow patterns around the swimmer. The results contribute to our understanding of drag-based propulsive systems and may influence the development of novel underwater robotic systems and limb prosthetic devices for underwater rehabilitation

Computational prediction of airfoil dynamic stall

The term dynamic stall refers to unsteady flow separation occurring on aerodynamic bodies, such as airfoils and wings, which execute an unsteady motion. The prediction of dynamic stall is important for flight vehicle, turbomachinery, and wind turbine applications. Due to the complicated flow physics of the dynamic stall phenomenon the industry has been forced to use empirical methods for its prediction. However, recent progress in computational methods and the tremendous increase in computing power has made possible the use of the full fluid dynamic governing equations for dynamic stall investigation and prediction in the design process. It is the objective of this review to present the major approaches and results obtained in recent years and to point out existing deficiencies and possibilities for improvements. To this end, potential flow, boundary layer, viscous-inviscid interaction, and Navier-Stokes methods are described. The most commonly used numerical schemes for their solution are briefly described. Turbulence models used for the computation of high Reynolds number turbulent flows, which are of primary interest to industry, are presented. The impact of transition from laminar to turbulent flow on the dynamic stall phenonmenon is discussed and currently available methods for it prediction are summarized. The main computational results obtained for airfoil and wing dynamic stall and comparisons with available experimental measurements are present. The review concludes with a discussion of existing deficiencies and possiblities for future improvements

Steady and unsteady internal flow computations via the solution of the compressible navier stokes equations for low mach numbers

Ph.D.Don P. Gidden

On the Prediction of Separation Bubbles Using a Modified Chen-Thyson Model

SEE ParentDocumentRecord|Ntt=20070038942 "Minnowbrook I: 1993 Workshop on End-Stage Boundary Layer Transition"; p. 269-281; NASA/CP-2007-214667The prediction of separation bubbles on NACA 65-213 and NACA 0012 using a modified Chen-Thyson transition model is presented. The contents include: 1) Background; 2) Analysis of NACA 65-213 separation bubble using cebeci's viscous-inviscid interaction method; 3) Analysis of NACA 0012 separation bubble using navier-stokes method; and 4) Comparison with experiment.Approved for public release; distribution is unlimited

Recent progress on high-order discontinuous schemes for simulations of multiphase and multicomponent flows

There have been growing research interests in high-order discontinuous schemes over recent years. With established theoretical basis and framework, more efforts have recently been taken to enable discontinuous-scheme capabilities for modeling complex multi-physical flows. Substantial achievements and milestones have been reached in the development of compatible numerical methods and algorithms that leverage high-order discontinuous schemes. The objective of this study is to comprehensively survey and summarize the key algorithmic components relevant to discontinuous schemes, while identifying the current state of the art in their capabilities for modeling multiphase and multicomponent flows. Furthermore, this review examines representative applications from recent literature to showcase the promising performance of discontinuous schemes in various scenarios. The review also identifies the limitations and bottlenecks encountered in previous research efforts and offers recommendations for future investigations. The primary aim of this review is to serve as a valuable guidebook for researchers in the field, facilitating the development of new computational fluid dynamics (CFD) capabilities based on discontinuous schemes