Haeseong Cho

A Computational Analysis for Flapping Wing by Coupling the Geometrically Exact Beam and Preconditioned Navier-Stokes Solution

In a flapping wing micro air vehicle (MAV), inspired by an organism of either insects or birds, flexibility of the wing structure induces a crucial effect upon the vehicle performance. Thus, in an analysis upon the flapping wing MAV, coupling between aerodynamics and structural dynamics considering the wing flexibility will be a critical component. This paper presents an accurate computational approach to simulate a flapping wing by coupling between CFD and CSD. Non-linear structural analysis based on the geometrically exact beam formulation was used. Such non-linear beam analysis was coupled with preconditioned Navier-Stokes solutions. For a grid deformation in the aerodynamic analysis, the mesh shearing methodology was used. A coupling between the structural and aerodynamic analyses was conducted by adopting the implicit coupling approach. After that, an aeroelastic analysis was performed and the results are compared with the experimental results. However, the flapping wing configuration is not slender in reality and their vein section geometry is complex generally. Thus, to consider those features, the finite element analysis, beam and shell, based on a co-rotational (CR) theory was developed in parallel. Currently, the CR beam analysis with a warping DOF was developed and validated by comparing it with NASTRAN in static condition.

All Eulerian method of computing elastic response of explosively pressurised metal tube

We present an all Eulerian approach to simulate the elastic response of a metal tube loaded explosively by a gaseous detonation. The high strain rate deformation of the metal tube subjected to high explosive detonation is mathematically described by hyperbolic processes where the characteristics of existing wave motions were correlated with the local particle velocities through the speed of sound in the metal. This is a favourable case for the hydrocode which is based on a compressible gas dynamics solver and for simulating a high strain rate and dominantly plastic response of a material subject to an explosive loading. The hydrocodes fall substantially short of predicting elastic motion without the plastic flow of the confining material, for relatively minor pressure loadings due to a gaseous explosion as opposed to a high explosive detonation of a charged tube. The corresponding loading pressure due to gaseous explosion is a few orders of magnitude lower than those resulting from high explosive loadings. Utilising a hydrocode designed to handle the reactive process leading to a plastic flow of the confining materials is of great interest and a significant challenge. The new technique, based on the Eulerian framework, preserves the feature of a Lagrangian code while utilising all the benefits of an Eulerian solver that uses fixed grids with the level-sets for defining the multi-material interfaces. The hybrid particle level-set algorithm is combined with a hydrodynamic solver that adds an elasticity correction when handling the structural response while the overall scheme remained hyperbolic during the entire reactive flow. Several unseen dynamics of detonation flow associated with the elastically loaded tube of finite thickness are reported by using the present method for analysing the highly pressurised vessel.

Parallel computation for three-dimensional shell analysis of curved configuration based on domain decomposition method

Abstract In this paper, a parallel computational algorithm is developed based on finite element tearing and interconnecting (FETI) method, specifically, localized Lagrange multipliers. The proposed FETI method decomposes large-size structures into non-overlapping subdomains via localized Lagrange multipliers. To consider the curved configuration of large-size structures, a facet shell element created by combining an optimal triangle membrane and discrete Kirchhoff triangle bending plate (OPT-DKT) is suggested and used by introducing rotational operators. Moreover, practical performance of the present OPT-DKT facet shell element is evaluated through static and dynamic analysis. Finally, parallel computation is implemented for the proposed approach using message passing interface (MPI).

Development of Nonlinear Structural Analysis Using Co-rotational Finite Elements with Improved Domain Decomposition Method

Recent advances in computational science and technologies induce increasing size of the engineering problems, and impact the fields of computational fluids and structural dynamics as well as multi-physics problems, such as fluid-structure interactions. At the same time, structural components used in many engineering applications show geometrically nonlinear characteristics. Therefore, development of effective solution methodologies for large-size nonlinear structural problems is required seriously in the fields of the mechanical and aerospace engineering. Especially, general finite element methods require a large number of elements in order to predict precise stress or deformation, resulting in increased computational costs due to enlarged computational time and memory requirement. Therefore, careful selection of grid size and solution methodology becomes important.

Design and analysis of the link mechanism for the flapping wing MAV using flexible multi-body dynamic analysis:

Recently, there has been an increase in the research on flapping wing vehicles which mimic biological motions. One result has been the flapping wing micro-aerial vehicle. In this paper, the design requirements for flapping wing micro-aerial vehicles were established through an analysis with the unsteady blade element theory. Then, based on the flapping wing micro-aerial vehicle design requirements, a flapping wing mechanism using a pair of six-bar linkage was devised. Moreover, several candidates for the present mechanism were analyzed using a flexible multi-body dynamic analysis to ensure the structural appropriateness of the mechanism. By completing such procedures, the performance of the present mechanism could be evaluated. A detailed design was then conducted. The structural analysis of the present mechanism was conducted regarding its flapping operation in a vacuum. The resulting von Mises stresses in the linkage were targeted to be smaller than the yield stresses of the chosen material. Next, additional details of the design and an experiment on the present flapping wing micro-aerial vehicle were conducted to validate its performance.

Analysis of two-dimensional improved finite element domain decomposition method using local and mixed Lagrange multipliers

This paper presents the two-dimensional structural computational algorithm based on the finite element domain decomposition technique. The proposed algorithm is compared with the well-known FETI approach with regard to convergence and efficiency characteristics. The proposed approach uses both local and global Lagrange multipliers together with an augmented Lagrangian formulation to achieve computational robustness and efficiency. The present algorithm is relatively simple and leads to improved convergence and efficiency characteristics. Numerical results are compared with those obtained by the original and dual-primal FETI methods to demonstrate the improved efficiency of the proposed approach. And implementation on a parallel computer is conducted for the proposed FETI methods. Finally, sparse matrix algorithm is implemented on the proposed FETI methods.

Helicopter Forward Flight Prediction using Geometrically Exact Beam Model and an Advanced Unsteady Aerodynamics

This paper presents a combination between the computational structural dynamic and aerodynamic analysis. In present computational model, geometrically exact beam formulation for the structural analysis and finite state dynamic inflow aerodynamics combined with blade element theory are used. The present beam formulation features advantages that displacements, inertial forces, and momenta can be directly extracted and solved simultaneously. Finite state dynamic inflow aerodynamics is used to predict induced inflow in forward flight. It calculates unsteady aerodynamics and will cost less computational time than the other wake models do. To combine those two analyses, a loosely coupled scheme is used. For the numerical analysis, both wind tunnel trim and free flight trim analyses are conducted. The present results are verified by comparing with those predicted by CAMRAD II.