Papers by Author: Yong Sheng Ren

Abstract: The effects of structural damping on the aeroelastic stability have been investigated for composite thin-walled blade. Structural model of the composite thin-walled blade exhibits bending-bending-twist coupling, with accounting for the presence of pretwist angle. The aerodynamic model used in the present paper is the differential dynamic stall model developed at ONERA. The structural damping of the blade is predicted based on the analytical formulas of the modal damping of thin-walled composite structure. The effect of structural damping on aeroelastic stability is taken into account by using proportional damping matrix. By means of Galerkin method, the nonlinear aeroelastic equations are reduced to ordinary equations. The general aerodynamic forces are obtained from strip theory. The resulting equations are then linearized for small perturbation about the equilibrium point and the stability characteristics are investigated through eigenvalue analysis and time domain integration.

Abstract: A geometrically nonlinear model for thin-walled, single-cell composite beams is developed by using variational formulation and the variational-asympotical method. The structural modeling is split into two parts: a two-dimensional analysis over the cross section, and a geometrically nonlinear analysis of a beam along the beam span. The nonlinear model is based on the assumption of moderate beam deflection, accounting for the pitch angle and extends the linear analysis model for anisotropic thin-walled beams. By employing the Galerkin’s method, an nonlinear algebraic equations is derived and then solved by means of an incremental Newton-Raphson method. Numerical results are obtained for one cantilevered box beam: Circumferentially Uniform Stiffness(CUS), under external load to investigate the effect of geometric nonlinearity and the effects of the fiber orientation, laminate stacking sequence, are also addressed.

Abstract: Based on a laminated composite structure, vibration and nonlinear stall aeroelastic stability of rotor blades modeled as anisotropic thin-walled closed-section beams are systematically addressed. The analysis is applied to a laminated construction of the circumferentially asymmetric stiffness (CAS) that produces bending-bending-twist coupling. The vibration characteristics of composite beam are determined by the Galerkin Method. The unsteady aerodynamic loads and centrifugal force are integrated with the nolinear aerodynamic model to deal with aeroelastic stability analysis. The influence of some related factors, pretwisted angle, ply-angle rotational speed, and wind speed, is investigated. The paper gives methods of eigenvalue analysis and aeroelastic response, which can determine the stability of the blade forced by the nolinear aerodynamics.

Abstract: The free vibration model of a rotating composite thin-walled closed-section beams is presented in this paper. The two-dimensional cross-sectional analysis based on the variational-asymptotical method(VAM) is combined with the Hamilton’s principle to derive the equations of motion and associated boundary conditions of the beams. The Galerkin method is employed in order to solve the coupled differential equations. The natural frequency results obtained for the present model are compared with those of the existing models. Numerical results are obtained for the laminated composite cantilevered box beam with Circumferentially Uniform Stiffness(CUS) configuration, the effects of the fiber orientation, pitch and precone on the natural frequencies associated with coupled vibration modes are investigated.

Abstract: The study performs the relation between the Lagrange multipliers and the constraint reaction forces in the multi-body systems. It helps to establish a simple and effective method to deal with the non-smooth factors including friction, contact and collision in multi-body systems. First, a general expression calculating the ideal constraint reaction forces is described by a form of complete Cartesian reference coordinate in a discrete dynamical system. Then, an explicit expression is given in the form of independent general generalized coordinates for a multi-body system. A condition under which the constraint reaction forces can be one-to-one corresponding to Lagrange multipliers is discussed. An example is used to demonstrate the process to realize the condition and the effectiveness of this method.

Abstract: The constitutive equations relating cross-sectional loads(forces and moments)to cross-sectional displacements(stretching, bending, twisting) of thin-walled laminated beams with integral shape memory alloy (SMA)active fibers was presented. The variational asymptotic method was used to formulate the force- deformation relationships equations, accounting for the presence of active SMA fibers distributed along the cross-section of the beam. The constitutive relationships for evaluation of the properties of a hybrid SMA composite ply were obtained following the rule of mixtures. The analytical expressions of the actuation components for the active beam were derived based on Tanaka’s constitutive equation and Lin’s linear phase transformation kinetics for SMA fiber. The general form of constitutive relation was applied to the case of stretching-twist coupling, corresponding to Circumferentially Uniform Stiffness (CUS). The present analysis extended the previous work done for modeling generic passive thin-walled laminated beams. Numerical results shown that significant stretching and twisting deflection occur during the phase transformation due to SMA actuation. The effects of temperature on structural response behavior during phase transformation from martensite to austenite are significant. The effects of the volume fraction of the SMA fiber, the martensitic residual strain and ply angle were also addressed