Altan Kayran

Free vibration analysis of laminated composite truncated circular conical shells

All components of translatory and rotatory inertia are included. The applicability of linear shell theory due to Reissner is assumed, and governing equations are solved for the natural frequencies and mode shapes by using a combination of modal iteration and transfer matrix approach for different boundary conditions

An Approach for the Evaluation of Effective Elastic Properties of Honeycomb Cores by Finite Element Analysis of Sandwich Panels

Different detailed finite element model alternatives are developed to come up with the most reliable finite element model of the sandwich panel, with the actual honeycomb core geometry, to evaluate the existing equivalent continuum models of aluminum honeycomb cores. Finite element models of sandwich panels with effective elastic constants of the honeycomb core are generated based on the existing continuum models of the honeycomb core. The evaluation of the effective elastic constants of honeycomb cores is based on the comparison of the total reaction forces, calculated by both finite element models, on the supported faces of sandwich panels due to different in-plane and out-of-plane uniform input displacements applied to the faces of the panels. The results show that the reliability of the individual in-plane and out-of-plane effective elastic constants of the existing continuum models of the honeycomb cores can be successfully evaluated based on the comparative study.

Torsional vibrations of layered composite paraboloidal shells

Abstract An analysis is presented for the torsional vibration characteristics of layered composite paraboloidal shells. The conditions for the uncoupling of the torsional modes from the bending and extensional modes are first determined for a layered shell of revolution. A finite difference scheme is developed for the solution of the resulting governing equation for the uncoupled torsional frequencies. The results of the finite difference solution for the paraboloids are compared with the analytical solution of uncoupled torsional frequencies of circular plates, in the limit as the curvature of the paraboloid goes to zero. As a result of the analysis of different paraboloids, the non-dimensional uncoupled torsional frequency parameters of the paraboloids are found to be inversely proportional to the ratio of the meridional arclength to the thickness of the paraboloid for a given edge angle.

Free-Vibration Analysis of Ring-Stiffened Branched Composite Shells of Revolution

Application of the multisegment numerical integration technique is extended to the free-vibration analysis of macroscopically anisotropic filament-wound branched shells of revolution with ring stiffeners, considering the variation of the thickness and winding angle. The solution procedure is based on a modified-frequency trial method, which processes on the numerically integrated transformed fundamental shell equations that are obtained in terms of finite exponential Fourier transform of the fundamental shell variables. The full macroscopically anisotropic form of the constitutive relations, including first-order transverse shear deformation and all components of translatory and rotary inertia, are included in the analysis. To handle branched shells of revolution, modifications that are necessary to incorporate junctions are added to the solution procedure. Inclusion of asymmetric circumferential stiffeners, with respect to the middle surface of the shell, into the semi-analytical solution method is demonstrated by presenting two alternative methods of analysis. The present solution methodology also incorporates the variation of the thickness and winding angle along the meridian of filament-wound shells of revolution, with general meridional curvature, by assuming placement of filaments along the geodesic fiber path on the surface of the shell of revolution.

Flight flutter testing and aeroelastic stability of aircraft

Purpose – To provide a general review of the flight flutter test techniques utilized in aeroelastic stability flight testing of aircraft, and to highlight the key items involved in flight flutter testing of aircraft, by emphasizing all the main information processed during the flutter stability verification based on flight test data.Design/methodology/approach – Flight flutter test requirements are first reviewed by referencing the relevant civil and military specifications. Excitation systems utilized in flight flutter testing are overviewed by stating the relative advantages and disadvantages of each technique. Flight test procedures followed in a typical flutter flight testing is described for different air speed regimes. Modal estimation methods, both in frequency and time domain, used in flutter prediction are surveyed. Most common flight flutter prediction methods are reviewed. Finally, key considerations for successful flight flutter testing are noted by referencing the related literature.Findings ...

A Method for the Calculation of Natural Frequencies of Orthotropic Axisymmetrically Loaded Shells of Revolution

The effect of transverse shear deformation is taken into account. The fundamental system of equations governing the free vibration of the stress-free shells of revolution are modified such that the initial stresses due to the axysymmetric loading are incorporated. The linear equation on the vibration about the deformed state are solved by using the transfer matrix method which makes use of the multisegment numerical integration technique. This method is commonly known as frequency trial method

Non-linear progressive failure analysis of open-hole composite laminates under combined loading

This article presents a finite element-based study of geometrically non-linear progressive failure analysis of open-hole composite laminates, subjected to combined in-plane and out-of-plane loading. Different ply- and constituent-based failure criteria and material property degradation schemes have been coded in Patran command language and a progressive failure analysis code is developed. Progressive failure analyses of the sample composite laminate, with an open-hole, subject to different combined loading are performed to study the effect of the geometric non-linearity on the first ply failure and progression of failure. For mode independent failure criteria, a method is proposed for the determination of separate degradation factors for fiber and matrix failures which are assumed to occur simultaneously. The results show that under combined in-plane and out-of-plane loading, depending on the load case linear analysis can significantly underestimate or overestimate the failure progression compared to the geometrically non-linear analysis even at low levels of out-of-plane loading.

Design, analysis and optimization of thin walled semi-monocoque wing structures using different structural idealization in the preliminary design phase

Purpose – In modeling an aircraft wing, structural idealizations are often employed in hand calculations to simplify the structural analysis. In real applications of structural design, analysis and optimization, finite element methods are used because of the complexity of the geometry, combined and complex loading conditions. The purpose of this paper is to give a comprehensive study on the effect of using different structural idealizations on the design, analysis and optimization of thin walled semi-monocoque wing structures in the preliminary design phase. Design/methodology/approach – In the design part of the paper, wing structures are designed by employing two different structural idealizations that are typically used in the preliminary design phase. In the structural analysis part, finite element analysis of one of the designed wing configurations is performed using six different one and two dimensional finite element pairs which are typically used to model the sub-elements of semi-monocoque wing st...

Analysis of Aircraft Survivability Against Fragmenting Warhead Threat

The article presents the methodology of the aircraft survivability analysis considering vulnerability of the aircraft against fragmenting warhead threat. The initial step of the survivability analysis against a fragmenting warhead threat is to position the target and the warhead in proper coordinate systems for the calculation of warhead-target engagement. Once the warhead detonates at a miss distance from the target, the motions of the fragments are calculated considering the drag and the gravity forces and the initial velocity of the fragments. For the hit calculations, the shotline method is employed, and hit locations, thickness and material information are obtained. For the shotline analysis, the functions and required libraries of the BRL-CAD software are integrated in the code which is used as the shotline subroutine of the main survivability analysis code developed in Fortran 90. Fragment penetration calculations are performed based on THOR equations, and vulnerability assessment of the aircraft against fragmenting warhead threats is carried out in terms of cumulative probability of kill of the aircraft considering all redundant and nonredundant critical components. Cumulative probability of kill calculations are performed according to the fault tree which is established for the particular aircraft being studied. Kill criteria for fuel tank fuel fire is presented. Survivability analysis of an aircraft against fragmentation warhead threat is performed by means of the developed code.

Effect of Stacking Sequence on Free Vibration Frequencies of Laminated Composite Circular Cylindrical Shells

This study compares the effect of stacking sequence on natural frequencies of cylindrical shells for different end conditions and vibration modes. For this purpose, an analysis of the natural frequencies of lam inated composite cylindrical shells is carried out using linear Reissner shell theory with the transverse shear deformation effects taken into account. The governing equations for the free vibration of laminated cylin drical shells are reduced to 10 first-order differential equations involving 10 unknowns. Natural frequencies and mode shapes are solved by using a combination of modal iteration and frequency trial methods for vari ous circumferential vibration modes, stacking sequences, and end conditions, including the nonconventional ones. The results show the efficient applicability of the combination of the modal iteration and frequency trial method to the solution of the shell vibration problem, and they give valuable information on the effect of the stacking sequence on the stiffness characteristics of composite cylindrical shells under different end conditions.