Nonlinear Flexible Multibody Dynamic Analysis of Rotor Blades with a Trailing Edge Flap

This study presents a novel nonlinear multibody approach for the structural modeling of helicopter blades. Unlike the conventional approach of using beam elements to represent the rotor blade, the present analysis utilizes a plate element, which assumes a nonlinear strain measure and rotation, as well as transverse shear deformation. The principle of virtual work is used to derive the equations of motion. Kinematic joints are modeled by a set of constraint equations, which are invoked in the formulation through the coordinate partitioning method. The capability of the present analysis is demonstrated by considering the structural dynamics response of a composite helicopter blade with a trailing edge flap. Composite materials are being extensively used in rotorcrafts, and an accurate analysis must include the effect of motion-induced stiffness in both the longitudinal (span-wise) and chord-wise directions and the coupling of the nonlinear elastic deformation with the overall dynamic motion. Most of the multibody dynamic analyses of rotor blades are limited to beam-type approximations. In a commonly accepted approach, the three-dimensional and geometrical nonlinear elasticity problem is reduced to two problems. 2 One is a geometrically nonlinear one- dimensional problem of a beam in the span-wise direction and the other is a two-dimensional linear elasticity problem from which the beam's cross-sectional properties at a span-wise station are determined. As required by this type of reduction, a number of blade models have emerged with various levels of refinement. These models have the advantage of being simple, and there is a significant reduction in the number of degrees of freedom as compared to a three-dimensional model without any reduction. However, the complete three-dimensional models do not involve any assumptions related to the modeling of the cross section, and no complicated post-processing technique is required to recover the complete displacement field. In order to achieve an optimum balance between accuracy and computational efficiency, this study utilizes a plate element for a complete three-dimensional analysis of the rotor blade. The model is able to capture all the necessary characteristics associated with composite rotor blades, such as transverse shear deformation, cross-section warping, and elastic coupling caused by material anisotropy and geometric nonlinearities. One of the major focus areas of the helicopter industry is to reduce the vibratory load at the source, before it propagates to the fuselage. Recently, the actively controlled trailing edge flap (ACF) has attracted much attention for