Papers by Vengalattore Nagaraj
The influence of concentrated inertias on the flutter characteristics of a uniform cantilever win... more The influence of concentrated inertias on the flutter characteristics of a uniform cantilever wing were investigated both by experimental and by theoretical methods. The experimental work consisted of wind tunnel tests on a segmented wing model on which concentrated masses in the shape of large pods could be mounted at a number of spanwise and chordwise positions. The weight of these pods was comparable to the weight of the bare wing, and their pitching moment of inertia was varied to values up to ten times the pitching moment of inertia of the bare wing. The influence of the spanwise and chordwise position of these pods on the flutter speed was investigated. In order to assess the influence of the aerodynamic shape of the pods, four different pods were tested, each having a different aerodynamic shape. The effect of adding horizontal fins to the trailing edge of the pods was also investigated as a means of increasing the aerodynamic damping and hence the flutter stability. [Continu...
The Atlas design team would like to acknowledge the following people and thank them for their val... more The Atlas design team would like to acknowledge the following people and thank them for their valuable assistance and guidance.
Collection of Technical Papers - AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference
ABSTRACT
44th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2003
ABSTRACT
49th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference <br> 16th AIAA/ASME/AHS Adaptive Structures Conference<br> 10t, 2008
Journal of The American Helicopter Society, 2008
ABSTRACT
Aiaa Journal, 2001
A re ned one-dimensional beam formulation based on a mixed approach has been developed for struct... more A re ned one-dimensional beam formulation based on a mixed approach has been developed for structural dynamics analyses of rotating and nonrotating composite beams and blades of general section shape with openor closed-section contours. The theory uses a mixed variational approach and accounts for the effects of elastic coupling, shell-wall thickness, warping, warping restraint, and transverse shear deformations. The analysis is validated against experimental data and other analytical results for composite cantilevered beams of various cross sections. Good correlation is achieved for all of the cases considered. The in uence of wall thickness and transverse shear on the free vibration characteristics of composite beams with either bending-torsion or extension-torsion coupling is investigated. For a bending-torsion coupled beam, the in uence of wall thickness becomes important when the thickness-to-depth ratio of the beam reaches about 30%. The frequency error in neglecting transverse shear exibility is about 50% for a bending-torsion coupled composite box beam with a slenderness ratio of 5.
Aiaa Journal, 2002
A re ned structural model based on a mixed force and displacement method is proposed for the anal... more A re ned structural model based on a mixed force and displacement method is proposed for the analysis of composite rotor blades with elastic couplings. The present formulation allows the modeling of either open-section or closed-section blades of arbitrary section shape, stacking sequence, and end restraint effects. The theory accounts for the effect of elastic couplings, shell wall thickness, section warping, warping restraint, and transverse shear deformations. A semicomplementary energy functional is used to derive, in a variationally consistent manner, the beam force-displacement relations. Bending and torsion related warpings and shear correction factors are obtained in closed form as part of the analysis. The resulting rst-order shear deformation theory (Timoshenko) describes the beam kinematics in terms of the axial, ap and lag bending, ap and lag shear, twist, and torsion-warping deformations. The theory is validated against experimental data and other nite element results for graphite-epoxy composite beams of various cross sections such as I sections, box sections, and two-cell airfoils. Good correlation is achieved for all of the test examples. The in uence of wall thickness and transverse shear on the static beam response is also investigated. Wall thickness effects are shown to become signi cant when the thickness-to-depth ratio of the beam reaches around 20%. The slenderness ratio has a signi cant effect on the transverse shear behavior of the beam, especially for beams with low slenderness ratios. It is also shown that the layup angle has a nonnegligible effect on the transverse shear behavior of the beam.
Journal of The American Helicopter Society, 1999
Journal of The American Helicopter Society, 2003
ABSTRACT
Journal of Aircraft, 1996
Journal of Aircraft, 2006
... successfully fabricated in-house, including a baseline rotor without coupling, two rotors wit... more ... successfully fabricated in-house, including a baseline rotor without coupling, two rotors with uniform spanwise flap-bending/torsion couplings, and two rotors with spanwise segmented flap-bending/torsion couplings. Bench-top and nonrotating dynamic tests were performed to ...
Aiaa Journal, 2001
A re ned one-dimensional beam formulation based on a mixed approach has been developed for struct... more A re ned one-dimensional beam formulation based on a mixed approach has been developed for structural dynamics analyses of rotating and nonrotating composite beams and blades of general section shape with openor closed-section contours. The theory uses a mixed variational approach and accounts for the effects of elastic coupling, shell-wall thickness, warping, warping restraint, and transverse shear deformations. The analysis is validated against experimental data and other analytical results for composite cantilevered beams of various cross sections. Good correlation is achieved for all of the cases considered. The in uence of wall thickness and transverse shear on the free vibration characteristics of composite beams with either bending-torsion or extension-torsion coupling is investigated. For a bending-torsion coupled beam, the in uence of wall thickness becomes important when the thickness-to-depth ratio of the beam reaches about 30%. The frequency error in neglecting transverse shear exibility is about 50% for a bending-torsion coupled composite box beam with a slenderness ratio of 5.
Journal of Aircraft, 1996
Aiaa Journal, 2002
A re ned structural model based on a mixed force and displacement method is proposed for the anal... more A re ned structural model based on a mixed force and displacement method is proposed for the analysis of composite rotor blades with elastic couplings. The present formulation allows the modeling of either open-section or closed-section blades of arbitrary section shape, stacking sequence, and end restraint effects. The theory accounts for the effect of elastic couplings, shell wall thickness, section warping, warping restraint, and transverse shear deformations. A semicomplementary energy functional is used to derive, in a variationally consistent manner, the beam force-displacement relations. Bending and torsion related warpings and shear correction factors are obtained in closed form as part of the analysis. The resulting rst-order shear deformation theory (Timoshenko) describes the beam kinematics in terms of the axial, ap and lag bending, ap and lag shear, twist, and torsion-warping deformations. The theory is validated against experimental data and other nite element results for graphite-epoxy composite beams of various cross sections such as I sections, box sections, and two-cell airfoils. Good correlation is achieved for all of the test examples. The in uence of wall thickness and transverse shear on the static beam response is also investigated. Wall thickness effects are shown to become signi cant when the thickness-to-depth ratio of the beam reaches around 20%. The slenderness ratio has a signi cant effect on the transverse shear behavior of the beam, especially for beams with low slenderness ratios. It is also shown that the layup angle has a nonnegligible effect on the transverse shear behavior of the beam.
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Papers by Vengalattore Nagaraj