New Optimization Strategy for Design of Active Twist Rotor

Abstract

This paper presents the development of a mixed-variable optimization framework for the aeroelastic analysis and design of active twist rotors. Proper tailoring of the blade properties can lead to the maximization of the active twist and the control authority for vibration reduction under operating conditions. Thus, using mathematical optimization, the cross-sectional layout is designed using continuous and discrete design variables for an active composite rotor blade to maximize the dynamic active twist while satisfying a series of constraints on blade cross-section parameters, stiffness, and strength. The optimization framework developed includes the Intelligent Cross-Section Generator as the cross-section and mesh generator, University of Michigan/Variational Asymptotic Beam Sectional analysis code for active cross-sectional analysis, and Rotorcraft Comprehensive Analysis Software for aeroelastic analysis of the active twist rotor blade. The optimization problem is solved using a surrogate-based approach in combination with the Efficient Global Optimization algorithm. In this paper, the results with mixed design variables are obtained with three different techniques and are compared with the results obtained using continuous design variables.= elastic modulus (where i is equal to 1, 2, and 3), N∕m 2 F z4 = amplitude of vertical force at the hub corresponding to 4∕rev frequency, N G ij = shear modulus, N∕m 2 M X = rolling moment at the hub in fixed frame, N · m M Y = pitching moment at the hub in fixed frame, N · m M 11 = mass per unit length, kg∕m R = blade radius, m S 44 = cross-sectional torsional stiffness, N · m 2 ε ij = cross-sectional strains θ i∕rev = amplitude of dynamic twist corresponding to i∕rev frequency (where i is equal to 3, 4, and 5), deg θ i∕rev;max = maximum amplitude of dynamic twist obtained from optimization at i∕rev actuation frequency (where i is equal to 3, 4, and 5), deg θ stat = static twist per unit length, deg ∕m θ 345∕rev = nondimensionalized amplitude of dynamic twist corresponding to 3, 4, and 5∕rev frequencies μ = advance ratio

New strategy for designing composite rotor blades with active flaps

“…In this section, only the best result obtained with mixed design variables is presented and compared with the result obtained using continuous design variables. A comparison between results obtained using the three mixed design variable optimization techniques and continuous design variable optimization is provided in Kumar and Cesnik (2013). The final results obtained for a flap located at 0.78R are shown in Table 7.…”

“…The design variables used are as follows: the chordwise location where the spar plies end (Spar End), chordwise location of the vertical spar web (Spar Web Loc), the two ballast masses (m 1 and m 2 ; see Figure 11), and the normalized ply thickness and ply angle for all the composite plies used in the cross section. Even though the baseline blade includes only one leading edge ballast mass, an additional ballast mass is used as the design variable since it is useful in tuning the dynamic properties of rotor blade, as observed in Kumar and Cesnik (2013). To make the rotor blade design more realistic, the location of the first ballast mass is fixed near the leading edge at x = 0.02c, while the second ballast mass is located just in front of the vertical spar web.…”

“…The optimization framework and strategy developed for the design of rotor blades with active twist, as described in Kumar and Cesnik (2013) and Kumar (2013), is extended for the design of composite rotor blades with active flaps in this article. The optimum blade design must aim to maximize the flap authority for vibration reduction while satisfying the constraints on the chordwise location of cross-sectional center of gravity (CG) and shear center (SC), blade mass per unit length, torsional frequency, blade strength, and so on.…”

Unified Approach for Accurate and Efficient Modeling of Composite Rotor Blade Dynamics The Alexander A. Nikolsky Honorary Lecture

“…This work served to demonstrate the capability to design optimally active rotor blades (Refs. 84,103,104).…”

Wind Turbine Blade Optimal Design Considering Multi-Parameters and Response Surface Method

“…In addition, in relation to the optimization of the blade design, many studies have already been conducted in helicopter and aeronautical engineering fields. Kumar and Cesnik [11] presented a mixed-variable optimization method for the aeroelastic analysis and design of active twist rotors. Sekula and Wilbur [12] identified the optimal blade tip planform for an active twist rotor.…”