SangJoon Shin

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...

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.

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.

Numerical simulation of actuation behavior of active fiber composites in helicopter rotor blade application

Smart structures incorporating active materials have been designed and analyzed to improve aerospace vehicle performance and its vibration/noise characteristics. Helicopter integral blade actuation is one example of those efforts using embedded anisotropic piezoelectric actuators. To design and analyze such integrally-actuated blades, beam approach based on homogenization methodology has been traditionally used. Using this approach, the global behavior of the structures is predicted in an averaged sense. However, this approach has intrinsic limitations in describing the local behaviors in the level of the constituents. For example, the failure analysis of the individual active fibers requires the knowledge of the local behaviors. Microscopic approach for the analysis of integrally-actuated structures is established in this paper. Piezoelectric fibers and matrices are modeled individually and finite element method using three-dimensional solid elements is adopted. Due to huge size of the resulting finite element meshes, high performance computing technology is required in its solution process. The present methodology is quoted as Direct Numerical Simulation (DNS) of the smart structure. As an initial validation effort, present analytical results are correlated with the experiments from a small-scaled integrally-actuated blade, Active Twist Rotor (ATR). Through DNS, local stress distribution around the interface of fiber and matrix can be analyzed.

Progressive failure analysis of carbon-fiber reinforced polymer (CFRP) laminates using combined material nonlinear elasticity and continuum damage mechanics based on treatment of coupon test

In this paper, predictions of the tensile strength of carbon-fiber reinforced polymer (CFRP) laminate composites are attempted using an improved continuum damage mechanics model with emphasis on the material nonlinearity of the fiber, shear stiffness reductions, the damage contribution of matrix cracks in adjacent layers, and the statistical distribution of the fiber strength due to defects. The Weibull parameter to establish a continuum damage mechanics model was extended to five parameters to satisfy multiscale compatibility and interlamina effects. These five Weibull parameters, which serve as coefficients of a damage evolution function, were investigated by using a statistical model of progressive tensile fiber failure in a composite laminate. The Newton–Raphson method was utilized to formulate a damage-estimation method via a progressive failure analysis procedure. A continuum damage analysis based on the Matzenmiller–Lubliner–Taylor model was revised to add the statistical characteristics of the material strength. The proposed continuum damage mechanics method was also used to solve laminate tension problems with various stacking sequences. The verification test articles include 16- and 20-ply IM7/8552, AS4/8552, and T700/M015 carbon/epoxy composite laminate un-notched and open-hole tensile specimens. The strength prediction of each laminate specimen is presented.

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.

Vibratory loads and response prediction for a high-speed flight vehicle during launch events

High-speed flight vehicles (HSFVs) such as space launch vehicles and missiles undergo severe dynamic loads which are generated during the launch and in in-flight environments. A typical vehicle is composed of thin plate skin structures with high-performance electronic units sensitive to such vibratory loads. Such lightweight structures are then exposed to external dynamic loads which consist of random vibration, shock, and acoustic loads created under the operating environment. Three types of dynamic loads (acoustic loads, rocket motor self-induced excitation loads and aerodynamic fluctuating pressure loads) are considered as major components in this study. The estimation results are compared to the design specification (MIL-STD-810) to check the appropriateness. The objective of this paper is to study an estimation methodology which helps to establish design specification for the dynamic loads acting on both vehicle and electronic units at arbitrary locations inside the vehicle.