Farhad Sabri

Finite Element Method Applied to Supersonic Flutter of Circular Cylindrical Shells

DOI: 10.2514/1.39580 The method of analysis is a combination of Sander’s thin shell theory and the classic finite element method, in which the nodal displacements are found from the exact solution of shell governing equations rather than approximatedbypolynomialfunctions.Pistontheorywithandwithoutacorrectionfactorforcurvatureisappliedto derive aerodynamic damping and stiffness matrices. The influence of stress stiffness due to internal pressure and axial loading is also taken into account. Aeroelastic equations in hybrid finite element formulation are derived and solved numerically. Different boundary conditions of the shell, geometries, and flow parameters are investigated. In all study cases, the shell loses its stability due to coupled-mode flutter and a traveling wave is observed during this dynamicinstability.Theresultsarecomparedwithexistingexperimentaldataandotheranalyticaland finiteelement solutions. The present study shows efficient and reliable results that can be applied to the aeroelastic design and analysis of shells of revolution in aerospace vehicles. Nomenclature � A� = coefficient matrix of shape functions; see Appendix B.1 a1 = freestream speed of sound � B� = coefficient matrix of strain vector; see Eq. (11) � Cf� = global aerodynamic damping matrix � cf�

Aerothermoelastic Stability of Functionally Graded Circular Cylindrical Shells

In this work, a hybrid finite element formulation is presented to predict the flutter boundaries of circular cylindrical shells made of functionally graded materials. The development is based on the combination of linear Sanders thin shell theory and classic finite element method. Material properties are temperature dependent, and graded in the shell thickness direction according to a simple power law distribution in terms of volume fractions of constituents. The temperature field is assumed to be uniform over the shell surface and along the shell thickness. First order piston theory is applied to account for supersonic aerodynamic pressure. The effects of temperature rise and shell internal pressure on the flutter boundaries of FG circular cylindrical shell for different values of power law index are investigated. The present study shows efficient and reliable results that can be applied to the aeroelastic design and analysis of shells of revolution in aerospace vehicles.Copyright

Modeling Flutter Response of a Flexible Morphing Wing for UAV

This paper is concerned with flutter instability of a novel morphing wing at low mission speeds for different morphing configurations. In view of the flexibility of the wing, it is highly desirable to determine the conditions that trigger flutter instability. Flutter boundary was predicted using the p-k method. Structural dynamics of the wing is obtained using lumped mass method and unsteady aerodynamic using the strip model is used to evaluate corresponding aerodynamic forces and moments. The results indicate that the newly designed flexible concept of the morphing wing increases the critical flutter velocity.

Effects of Sloshing on Flutter Prediction of Partially Liquid-Filled Circular Cylindrical Shells

Dynamic stability of liquid-filled circular cylindrical shell subjected to supersonic flow and influenced by a moving inside fluid-free surface is investigated simultaneously. Structural modeling is based on the combination of Sanders thin shell theory and the standard finite element method. The shape functions are found from exact solution of shell theory which yields fast and precise convergence. First-order piston theory was applied to derive aerodynamic damping and stiffness matrices coupled with the shell elastic deformation. The fluid inside the shell is modeled as a potential variable at each node of the structure elements and its motion is expressed in terms of nodal degrees of freedom at the interface of the fluid and shell. Effect of axial loading is also investigated by developing a geometrical stiffness matrix. Results showed that ignoring the fluid sloshing effect leads to over-prediction of critical flutter velocities and the most significant deviations are found for short and wide shells with high values of liquid filling ratios. This hybrid numerical-analytical software package can be used effectively for aeroelastic analysis and design of shells of revolution at less computational cost compared to commercial finite element packages.

In-Flight Ice Accretion Simulation In SLD Conditions

This paper presents the capability of CANICE (2D and 3D) codes to simulate ice accretion in the supercooled large droplets (SLD) conditions. Icing simulation for different MVD, larger and smaller than SLD threshold has been performed with CANICE2D and 3D. A tentative empirical splashing model was implemented in the CANICE3D code to account for the mass loss due to water droplets splashing. This was applied to a MS(1)-317 wing for a droplet size of 92 microns. The predicted results for water collection efficiency were in good agreement with the experimental data. In the analyzed case the model that was used demonstrated the capability to predict the splashing effects quite well near the stagnation point, where the normal component of the impact velocity has the largest value.