Evaluation of effective elastic properties of honeycomb sandwich structures by optimization involving modal behavior

Çınar, Okan
This thesis aims to develop an alternative approach which estimates the effective elastic properties of 2D orthotropic equivalent model of the honeycomb core material. For this purpose, 3D detailed finite element (FE) model of honeycomb structure, with the actual cell geometry and the face sheets, is used as the reference structure. Effective elastic properties of the equivalent 2D orthotropic model, representing the honeycomb core, are determined by means optimization. The objective function of the optimization is defined as the minimization of the error function expressed as the difference of the natural frequency results of certain number of modes of the reference 3D detailed FE model and the equivalent model of the sandwich structure with the honeycomb core. The effective material properties of the 2D orthotropic equivalent model of the honeycomb core are used as the design variables to optimize. The genetic algorithm that available in MATLAB Optimization Toolbox is used as optimizer, and MSC Nastran is used as the finite element solver to perform the modal analysis of the sandwich plates with honeycomb material as the core. Optimizer and the finite element solver are coupled by means of an interface code which is developed in the MATLAB environment. The studies in the literature, in which the effective material properties of the orthotropic equivalent model are estimated analytically, are also used for comparison purposes. Moreover, the effective material properties predicted analytically are used as the initial population of the optimization in genetic algorithm. The results show that developed approach predicts more accurate orthotropic effective material properties for the honeycomb than the present analytical models predict.


Analysis of RC walls with a mixed formulation frame finite element
Sarıtaş, Afşin (2013-10-01)
This paper presents a mixed formulation frame element with the assumptions of the Timoshenko shear beam theory for displacement field and that accounts for interaction between shear and normal stress at material level. Nonlinear response of the element is obtained by integration of section response, which in turn is obtained by integration of material response. Satisfaction of transverse equilibrium equations at section includes the interaction between concrete and transverse reinforcing steel. A 3d plastic...
Questioning Degree of Accuracy Offered by the Spectral Element Method in Computational Electromagnetics
Mahariq, I.; KURT, HAMZA; Kuzuoğlu, Mustafa (2015-07-01)
In this paper, a comparison amongst the spectral element method (SEM), the finite difference method (FDM), and the first-order finite element method (FEM) is presented. For the sake of consistency, the comparison is carried out on one-dimensional and two-dimensional boundary value problems based on the same measure of error in order to emphasize on the high accuracy gained by the SEM. Then, the deterioration in the accuracy of the SEM due to the elemental deformation is demonstrated. Following this, we try ...
Simulation of Directional Microphones in Digital Waveguide Mesh-Based Models of Room Acoustics
Hacıhabiboğlu, Hüseyin; Günel Kılıç, Banu (2010-02-01)
Digital waveguide mesh (DWM) models are time-domain numerical methods providing computationally simple solutions for wave propagation problems. They have been used in various acoustical modeling and audio synthesis applications including synthesis of musical instrument sounds and speech, and modeling of room acoustics. A successful model of room acoustics should be able to account for source and receiver directivity. Methods for the simulation of directional sources in DWM models were previously proposed. T...
Assessment and improvement of elementary force computations for cold forward rod extrusion
Ocal, M; Egemen, N; Tekkaya, AE (2005-06-01)
Two commonly used analytical force computation methods for cold forward rod extrusion are evaluated by means of precise finite element computations. The upperbound model by Avitzur based on the spherical velocity field and the model by Siebel based on a quasi-upper-bound solution are considered. It has been found that the pure deformation forces obtained by summing the ideal force and shear force terms deviate between +25% and -20% from the finite element solutions. Larger deviations, however, occur for the...
On the accuracy of first-order numerical derivatives in multidimensional digital waveguide mesh topologies
Hacıhabiboğlu, Hüseyin; Günel Kılıç, Banu (2008-01-01)
Digital waveguide mesh (DWM) models are numerical solvers for the wave equation in N-dimensions. They are used for obtaining the traveling-wave solution in practical acoustical modeling applications. Although unstructured meshes can be used with DWMs, regular mesh topologies are traditionally used due to their implementation simplicity. This letter discusses the accuracy of first-order approximations to numerical derivatives on more general unstructured mesh topologies. The results are applied to structured...
Citation Formats
O. Çınar, “Evaluation of effective elastic properties of honeycomb sandwich structures by optimization involving modal behavior,” M.S. - Master of Science, Middle East Technical University, 2014.