JunYoung Kwak

Computational approaches for large scale structural analysis using domain decomposition technique

This paper describes application of an improved computational approach based on domain decomposition technique for a large scale structural analysis. We compared computational algorithms corresponding to the original and an improved FETI approach. In the original FETI approach, Lagrange’s multipliers were introduced to enforce compatibility at the interface DOF’s. Specifically, we adopted local Lagrange’s multipliers with an augmented Lagrangian formulation (ALF) as penalty formulation of the problem to improve computational robustness and efficiency. For validation of the present approach, we compared its results with those obtained by the original FETI. Practical performances of the present approach were demonstrated through several 2-D plane and 3-D shell static analysis results.

Flapping-Wing Fluid–Structural Interaction Analysis Using Corotational Triangular Planar Structural Element

In this paper, a triangular planar element is developed for a geometrically nonlinear structural analysis, which includes the drilling degrees of freedom using a corotational framework. Based on the assumptions of a small degree of strain and large displacement, the corotational framework allows an accurate geometrically nonlinear structural analysis. The presently improved corotational framework accommodates in-plane rotational behavior (that is, the drilling degrees of freedom) by using the corotational framework corresponding to a solidlike planar element. It focuses on triangular planar elements that will be useful for three-dimensional analysis using a reduced number of degrees while targeting a structure with a complex geometry, such as a flapping wing. Regarding the present analysis, validation by solving both static and time-transient problems is conducted. The fluid–structure interaction framework is then developed by using the present structural analysis. During this validation procedure, the pr...

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.

Domain Decomposition Approach Applied for Two- and Three-dimensional Problems via Direct Solution Methodology

This paper presents an all-direct domain decomposition approach for large-scale structural analysis. The proposed approach achieves computational robustness and efficiency by enforcing the compatibility of the displacement field across the subdomain boundaries via local Lagrange multipliers and augmented Lagrangian formulation (ALF). The proposed domain decomposition approach was compared to the existing FETI approach in terms of the computational time and memory usage. The parallel implementation of the proposed algorithm was described in detail. Finally, a preliminary validation was attempted for the proposed approach, and the numerical results of two- and three-dimensional problems were compared to those obtained through a dual-primal FETI approach. The results indicate an improvement in the performance as a result of the implementing the proposed approach.

Development of Finite Element Domain Decomposition Method Using Local and Mixed Lagrange Multipliers

In this paper, a finite element domain decomposition method using local and mixed Lagrange multipliers for a large scal structural analysis is presented. The proposed algorithms use local and mixed Lagrange multipliers to improve computational efficiency. In the original FETI method, classical Lagrange multiplier technique was used. In the dual-primal FETI method, the interface nodes are used at the corner nodes of each sub-domain. On the other hand, the proposed FETI-local analysis adopts localized Lagrange multipliers and the proposed FETI-mixed analysis uses both global and local Lagrange multipliers. The numerical analysis results by the proposed algorithms are compared with those obtained by dual-primal FETI method.

Transient Time Aeroelastic Analysis for a Supersonic Flight Vehicle with a Ramjet Engine

This paper presents a transient time aeroelastic analysis for a supersonic flight vehicle with a ramjet engine. First, computational fluid dynamics (CFD) is conducted to estimate its baseline geometry and the prediction results obtained upon the vehicle surface are transferred to the structural transient time analysis. The structural analysis is then carried out. A brand new finite element domain decomposition structure analysis is developed for the present transient time aeroelastic analysis. To solve a resulting large-scale system equation, FETI method is adopted for the present shell analysis. And comparison results between the present transient time FETI and Dual-primal FETI methods are attempted. During the 500 time steps, both analyses show good agreement with a difference less than 0.01% for the example problem. As a result, a detailed analytical procedure for the transient time aeroelastic analysis is established to predict a possibility of an excessive deformation or buckling induced in the supersonic vehicle during flight.