Composite Rotor Research Articles

자유후류기법을 이용한 무힌지 로터 시스템의 정지비행시 정적 공탄성 해석

본 연구에서는 자유후류기법을 이용하여 복합재 무힌지 로터 블레이드에 대한 정적 공탄성 해석을 수행하였다. 1차원 보의 거동을 해석하기 위하여 대변형 보 이론이 적용되었다. 또한, 복합재 블레이드의 단면 해석을 위하여 이방성 보 이론이 적용되었다. 공탄성 해석에 필요한 공력 하중들은 와류격자법(VLM)에 기초한 3차원 공기력 모델을 통하여 계산되었다. 이때, 정지비행시의 후류는 순차적 시간 적분 자유후류법을 통하여 묘사되었다. 복합재 무힌지 로터 블레이드의 정적 변형에 대한 해석 결과를 2차원 준정상 공기력과 경험후류기법을 통한 해석 결과들과 비교하여 살펴보았다. 결과적으로, 정지비행시 후류 효과에 의해 정적 변형의 결과가 달라짐을 확인하였다. The static aeroelastic analysis of composite hingeless rotor blades in hover was performed using free-wake method. Large deflection beam theory was applied to analyze blade motions as a one-dimension beam. Anisotropic beam theory was applied to perform a cross-sectional analysis for composite rotor blades. Aerodynamic loads were calculated through a three-dimensional aerodynamic model which is based on the unsteady vortex lattice method. The wake geometry in hover was described using a time-marching free-wake method. Numerical results of the steady-state deflections for the composite hingeless rotor blades were presented and compared with those results based on two-dimensional quasi-steady strip theory and prescribed wake method. It was shown that wakes affect the steady-state deflections.

Quality Evaluation of Resin Transfer Molded Products

The present study introduces a new procedure to evaluate the quality of composite products using the graph theoretic approach, and a composite screw rotors process is considered (manufactured by the Resin Transfer Molding (RTM)). The composite product coming from the manufacturing processes must have good surface finish and high quality without any defects. There are several factors which affect the quality during design and manufacture of the RTM products like screw rotors. These factors form a quality digraph based on the interactions existing between them. Hence, we considered the quality digraph by defining fuzzy crisp scores for the degree of interactions between the factors. A quality index derived from quality permanent function is helpful for quality inspectors on the shop floor to decide whether the product is within benchmark limits. The benchmark limits obtained for the composite product, manufactured by the RTM process by considering the strong and weak interactions existing between the factors defined for quality, are considered as upper and lower bounds in deriving the indices. Therefore the present work proposes a quality index, which is a useful numerical index for quality assurance groups to take proper decisions on the shop floor for the manufacturing process adapted to composites (composite molders).

Cross-Sectional Design of Composite Rotor Blades

An important step of rotor blade design is to design cross-sections that possess specified stiffness and inertia properties. This paper describes an innovative methodology for Based on a paper presented at the 63 Annual Forum of the American Helicopter Society, Virginia Beach, Virginia, May 1 – 3, 2007.

Support Vector Machine based Online Composite Helicopter Rotor Blade Damage Detection System

This work explores a feasibility of using vibratory hub loads and support vector machine (SVM) to predict damage and hence the life consumption of the composite helicopter rotor blade. Generally, the initial part of the composite's life is dominated by matrix cracking; the intermediate part by debonding/delamination and the final failure due to fiber breakage. The simulated hub loads under various damage levels are obtained using a comprehensive aeroelastic analysis of the composite rotor blade with physics based damage modes and are then linked with the life consumption of the blade using a phenomenological model. The SVM is used for classification of the useful life of the blade into three classes which are useful to decide the prognostic action. The performance of the blade damage detection system is demonstrated using simulated hub loads obtained using a two-cell airfoil section representing the stiff-inplane blade. The model based hub load variations are contaminated with noise to simulate the real data. It is observed that the SVM based damage detection system is more robust, reliable and easy to implement than the rotating frame measurement based methods.

Fluid-Structure Coupled Analyses of Composite Wind Turbine Blades

The composite rotor blades have been widely used as an important part of the wind power generation systems because the strength, stiffness, durability and vibration of composite materials are all excellent. In composite laminated blades, the static and dynamic aeroelasticity tailoring can be performed by controlling laminate angle or stacking sequence. In this paper, the fluid-structure coupled analyses of 10kW wind turbine blades has been performed by means of the full coupling between CFD and CSD based finite element methods. Fiber enforced composites fabricated with three types of stacking sequences were also studied. First the centrifugal force was considered for the nonlinear static analyses of the wind turbine so as to predict the deformation of tip point in the length direction and maximum stress in the root of a wind turbine. And then, the aeroelastic static deformation was taken into account with fluid-structure interaction analysis of the wind turbine. The Arbitrary Lagrangian Eulerian Coordinate was used to compute fluid structure interaction analysis of the wind turbine by using ADINA program. The displacement and stress increased apparently with the increment of aerodynamic force, but under the condition of maximum rotation speed 140RPM of the wind turbine, the displacement and stress were in the range of safety.

틸트로터 항공기 복합재료 날개의 진동 제어

Mathematical modeling and vibration control of a tiltrotor aircraft composite wing-rotor system are investigated in this study. A wing-mounted rotor can be tilted from the vertical position to a horizontal one, and vice versa. Effect of vibration control of the wing-rotor system via piezoelectricity is studied as a function of tilt angle, ply angle of composite wing and rotor`s spin speed. Composite wing is modeled as a thin-walled box beam having a circumferentially uniform stiffness configuration that produces elastic coupling between flap-lag and between extension-twist behavior. Numerical simulations are provided and pertinent conclusions are outlined.

Fuzzy-Logic-Based Health Monitoring and Residual-Life Prediction for Composite Helicopter Rotor

A health-monitoring and life-estimation strategy for composite rotor blades is developed in this work. The cross-sectional stiffness reduction obtained by physics-based models is expressed as a function of the life of the structure using a recent phenomenological damage model. This stiffness reduction is further used to study the behavior of measurable system parameters such as blade deflections, loads, and strains of a composite rotor blade in static analysis and forward flight. The simulated measurements are obtained using an aeroelastic analysis of the composite rotor blade based on the finite element in space and time with physics-based damage modes that are then linked to the life consumption of the blade. The model-based measurements are contaminated with noise to simulate real data. Genetic fuzzy systems are developed for global online prediction of physical damage and life consumption using displacement- and force-based measurement deviations between damaged and undamaged conditions. Furthermore, local online prediction of physical damage and life consumption is done using strains measured along the blade length. It is observed that the life consumption in the matrix-cracking zone is about 12-15% and life consumption in debonding/delamination zone is about 45-55% of the total life of the blade. It is also observed that the success rate of the genetic fuzzy systems depends upon the number of measurements, type of measurements and training, and the testing noise level. The genetic fuzzy systems work quite well with noisy data and are recommended for online structural health monitoring of composite helicopter rotor blades.

Numerical evaluation of the aerodynamic influence of the helicopter composite blade trailing edge tabs

In classical composite helicopter rotor blade production, a small flat tab must be formed along the entire trailing edge, in order to enable proper merging of the upper and the lower surface plies during manufacturing. By this, the original airfoil shape is altered. Such fixed tabs have been added in a range of possible angular positions to several existing asymmetrical helicopter airfoils, and their capability to change the moment coefficient about the aerodynamic center of the airfoils was initially analyzed. Although usual tabs are proportionally small, angular domains in which they do not remarkably change the required nearly zero aerodynamic moment, were quantified as very narrow. In the next stage, an algorithm has been defined and implemented: (a) for the determination of optimum angular tab positions for several asymmetrical airfoils, that satisfy the moment requirement (for such airfoils optimum tab direction cannot be known in advance), and (b) for the reduction of the influence of eventual inherent numerical errors of applied software to a minimum. The accuracy of this algorithm has been verified on a symmetrical airfoil, for which the optimum tab position is readily known. In the next step, the tab influence on other aerodynamic airfoil characteristics, and the influence on flight performance of a light helicopter from an on-going project, has been analyzed. Several possible tab design concepts were defined, and some characteristic aspects of their implementation were considered. At the level of preliminary helicopter performance calculations, the influence of the two general outcomes of the tab designs were analyzed, one that preserves initial relative airfoil thickness, and another which leads to its reduction. In the first case, the influence of the slight increase of drag coefficient was taken into account, while in the second one, the decrease of drag coefficient, accompanied with necessary additional strengthening and added blade mass was considered. In both cases applied modifications proved to have moderate direct influence on helicopter flight performance, compared with a hypothetic case that the original airfoil without tab could have been used instead. General conclusions have imposed the need for very careful approach in tab design for asymmetrical airfoils, which must be primarily focused on the tab’s potential remarkable influence on the aerodynamic moment.

A rigorous, engineer‐friendly approach for modelling realistic, composite rotor blades

AbstractA rigorous approach is presented for the modelling of composite beam structures of the type encountered in wind turbine blades, helicopter rotor blades and the like. The analysis methodology is based on a dimensional reduction of the geometrically nonlinear, three‐dimensional, anisotropic theory of elasticity. Small parameters stemming from the beam‐like geometry of slender structures such as wind turbine blades lead to a splitting of the problem into a (usually) linear, two‐dimensional cross‐sectional analysis and a geometrically exact nonlinear, one‐dimensional beam analysis. The incorporation of such beam analyses into flexible multibody codes presents a unified and powerful approach to the modelling of wind turbines with composite rotor blades. The generality and power of the methodology are illustrated in several examples. Copyright © 2006 John Wiley &Sons, Ltd.

Design and Spin Test of a Hybrid Composite Flywheel Rotor with a Split Type Hub

A study is conducted on lowering the radial tensile stresses and increasing the performance of the fiber wound composite flywheel rotor by applying pressure on the inner surface of the rotor using a split type hub that spreads in the radial direction due to the centrifugal force. A conventional solid or ring type hub in most cases produces tensile stresses within the rotor, possibly causing delamination and eventually lowering the maximum speed of the rotor. The relationship between the stresses of the rotor and the thickness of the hub is derived and applied to the single and hybrid rotors. A hybrid composite rotor of 180 mm inner diameter and 340 mm outer diameter is designed and fabricated, which reaches only the strength ratio of 0.58 at the maximum rotating speed of 40,000 rpm. A spin test was conducted to show the improved performance of the rotor with the split type hub by measuring the mechanical strains from the rotor. The radial and circumferential strains at four different locations are measured up to 30,000 rpm using a wireless telemetry system, and they are in good agreement with the analytical calculations. The rotor has survived a spin test of up to 40,000 rpm, which corresponds to the usable energy of at least 500 W h with the safety factor of 1.7.

Genetic fuzzy system for online structural health monitoring of composite helicopter rotor blades

A structural health monitoring (SHM) methodology is developed for composite rotor blades. An aeroelastic analysis of composite rotor blades based on the finite element method in space and time and with implanted matrix cracking and debonding/delamination damage is used to obtain measurable system parameters such as blade response, loads and strains. A rotor blade with a two-cell airfoil section and [ 0 / ± 45 / 90 ] s family of laminates is used for numerical simulations. The model based measurements are contaminated with noise to simulate real data. Genetic fuzzy systems (GFS) are developed for global online damage detection using displacement and force-based measurement deviations between damaged and undamaged conditions and for local online damage detection using strains. It is observed that the success rate of the GFS depends on number of measurements, type of measurements and training and testing noise level. The GFS work quite well with noisy data and is recommended for online SHM of composite helicopter rotor blades.

Sliding‐mode control for speed sensorless induction machine drive using an adaptive nonlinear rotor flux observer

PurposeTo propose and adaptive nonlinear controller for adjustable speed sensorless induction motor drive, using a novel adaptive rotor flux observer. The adaptive flux observer scheme in this paper provides the simultaneous estimation of the rotor speed, rotor resistance and stator resistance.Design/methodology/approachThe IM rotor speed and rotor flux controllers are designed based on combination of input‐output feedback linearizing, linear optimal feedback control and sliding‐mode (SM) control methods. In addition a novel adaptive rotor flux observer is designed based on Lyapunov theory. The proposed control method is tested by simulation and experimental results.FindingsThe composite rotor speed and rotor flux observer in combination with adaptive rotor flux scheme guarantees a perfect speed, torque and flux tracking control for the IM sensorless drive.Research limitations/implicationsThe proposed control method has a drawback in the IM low speed operating region. Additional research may be able to solve this problem as well as should analyze the sensitivity of the IM drive system performance with respect to variation of the system controller and adaptive flux observer gains. In addition, this research should also analyze the influence of sampling rate, truncation errors, measurement noise, simplifying model assumption and magnetic saturation.Practical implicationsThe proposed control method can be used for adaptive and robust control of the IM drive where an optimal efficiency is desired subject to the variable load torque demand.Originality/valueBased on Lyapunov theory, a novel adaptive rotor flux observer is introduced in which the rotor speed, rotor resistance and stator resistance are treated as the unknown constant parameters.

Development of Mach Scale Rotors with Tailored Composite Coupling for Vibration Reduction

This paper presents the design, structural and aeroelastic analyses, fabrication, and structural tests of Mach-scale articulated composite rotors with tailored flap-bending/torsion couplings for vibration reduction. The rotor design was nominally based on the UH-60 Black Hawk rotor. A new fabrication process was developed to manufacture Mach-scale composite tailored blade. Five sets of Mach-scale composite tailored rotors were 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 verify the structural analysis of these composite tailored blades. The measured results correlated well with predictions. Comprehensive aeroelastic analysis (using University of Maryland Advanced Rotorcraft Code) of these Mach-scale composite tailored rotors indicated that blade elastic flap-bending/ torsion couplings can significantly impact rotor vibration characteristics. It was shown that spanwise segmented flap-bending/torsion couplings can provide larger rotor vibration reduction than uniform spanwise couplings.

On the effect of progressive damage on composite helicopter rotor system behavior

Composite rotor blades are routinely used in modern helicopters. Damage in composite helicopter rotor blades is investigated in this work. Effects of the key damage modes in composite materials such as matrix cracking, debonding/delamination and fiber breakage on various properties of the composite rotor blade such as stiffnesses, frequencies, deflection, root forces, root moments and strains in forward flight are studied using an aeroelastic analysis. The composite rotor blade is modeled as a thin walled composite beam and includes the effect of transverse shear, elastic couplings and restrained warping. Matrix cracking is modeled at the laminate level and debonding/delamination and fiber breakage at the lamina level and included in the formulation by adjusting the A, B and D matrices for composite laminates. A stiff in-plane rotor blade with a two-cell airfoil section with [0/±45/90] s family of laminates is considered. An aeroelastic analysis of the helicopter rotor based on finite elements in space and time is used to study the effects of key damage modes in a composite rotor in forward flight.

Optimization of a Composite Rotor Blade using a Genetic Algorithm with Local Search

The material and ply angles of a fiber-reinforced plastic (FRP) rotor blade of a helicopter are optimized using a genetic algorithm (GA) with local search. The variation of the structural stiffness with material and ply angle is investigated. The aim of the optimization is to find an optimal stacking sequence that minimizes twist deformation. An optimum rotor blade is obtained using the ply angles as variables; failure, natural frequency, and minimum moment of inertia are used to constrain the optimization. The GA is employed as an optimization tool. A simplified local search is implemented in the final stage of optimization to reduce the searching time.

Modeling Multi-Layer Matrix Cracking in Thin Walled Composite Rotor Blades

Helicopter rotor blades are made of fiber-reinforced composite materials that are prone to matrix cracking. Matrix cracking precedes more serious damage mechanisms such as delamination and fiber breakage and is therefore a useful indicator of structural health. In the present study, the effect of matrix cracking on composite blade stiffness and deflections is investigated. A stiff inplane rotor blade with a rectangular box and two-cell airfoil section with [0/ +/-45/90], family of laminates is considered. It is observed that the stiffness decreases rapidly in initial phase of matrix cracking and then becomes saturated. Study of the behavior of composite rotor blade from matrix cracking in single, two and complete lamina group show a bending stiffness loss of 6-12 percent and a torsion stiffness loss of 25-30 percent at the point where matrix cracking saturates, and more severe forms of damage such as debonding/delamination and fiber breakage begin.

Investigation of windage splits in an enclosed test fixture having a high-speed composite rotor in low air pressure environments

The University of Texas at Austin Center for Electromechanics (UT-CEM) has designed and conducted a series of composite rotor spin tests to measure the windage losses and temperature distributions of a test setup at high rotor speeds and low air pressures. The intent of the windage tests is to validate the windage loss predictions and investigate how the air-gap windage is distributed between the rotor and stator. The findings of the spin tests will then be used to perform windage-related thermal design and analysis of a high-speed electrical machine. The radial air-gap flows under the test conditions, a low rotor cavity air pressure of 1 torr and high rotor surface velocities of 333 and 614 m/s, were in a laminar flow regime. Transient rotor and stator finite-element thermal analyses, using the measured windage losses and predicted laminar-flow windage splits, have been carried out to analyze the rotor and stator temperature distributions. This paper shows the detailed thermal analysis and compares the predictions with the measurements. The predicted and measured transient rotor and stator temperatures are in good agreement.

Splits of windage losses in integrated transient rotor and stator thermal analysis of a high-speed alternator during multiple discharges

For a high-speed electrical alternator, the rotor outer banding and stator inner liner are typically made of high strength graphite epoxy composites due to their high strength and stiffness. Machine structural integrity at high rotating speeds degrades significantly as the composite resins lose their strength at high temperatures. The magnitude of the frictional windage losses generated in the air gaps and the splits of the windage losses between the rotor and stator become crucial to the machine design since these windage losses greatly influence the rotor outer and stator inner surface temperatures. Splits of windage losses generated by an enclosed high-speed composite rotor in low air pressure environments were investigated by The University of Texas at Austin Center for Electromechanics and described in a companion paper. The windage splits are dictated by the air temperature gradients at the rotor outer and stator inner surfaces. Unique heating, cooling, and component material properties of a typical high-speed alternator during repetitive-discharge events make its transient air-gap windage splits very much different from those of the test setup. This paper describes transient windage splits in integrated rotor and stator thermal analyses of a high-speed alternator designed for multiple discharges. The transient windage splits in the air-gap air flow were obtained through multiple iterations on windage losses, air-gap air temperatures, and rotor and stator surface temperatures.

무힌지 로터 블레이드의 허브하중에 대한 복합재료 연성거동 연구

본 연구에서는 전진비행시 무힌지 로터 블레이드의 허브하중에 대한 복합재료 연성의 영향을 고찰하였다. 무힌지 복합재료 로터 블레이드를 단일 상자형 보로 모델링 하였으며, 전단 변형 및 비틀림 워핑과 같은 비고전적 효과를 고려하였다. 운동방정식은 해밀턴의 원리를 이용하여 구성하였으며, 로터 블레이드의 공간 및 시간차원에서의 유한요소법을 적용하여 완전평형해석을 수행하였다. 블레이드에 작용하는 공기력은 2 차원 준정상 공기력 이론을 바탕으로 하여 역류 및 압축성 효과를 고려하였다. MSC/NASTRAN을 이용하여 피치 -플랩 및 피치-래그와 같은 탄성 연성의 크기를 구하고, 고전적인 기하학적 연계와 비교하였다. 탄생 연성은 <TEX>$N_b/rev$</TEX> 허브하중의 특성에 적지 않은 영향을 미침을 확인하였다 블레이드 복합재료의 적층각을 적절히 변화시킬 경우 약 10-40%의 허브하중을 감소시킬 수 있음을 보였다. In this work, the effect of composite couplings on hub loads of a hingeless rotor in forward flight is investigated. The hingeless composite rotor blade is idealized as a laminated thin-walled box-beam. The nonclassical effects such as transverse shear, torsional warping are considered in the structural formulation. The nonlinear differential equations of motion are obtained by applying Hamilton's principle. The blade response and hub loads are calculated using a finite element formulation in space and time. The aerodynamic forces acting on the blade are calculated by quasi-steady strip theory. The theory includes the effects of reversed flow and compressibility. The magnitude of elastic couplings obtained by MSC/NASTRAN is compared with the classical pitch-flap <TEX>$({\delta}3)$</TEX> or <TEX>$pitch-lag({\alpha}1)$</TEX> coupling. It is found that the elastic couplings have a substantial effect on the behavior of <TEX>$N_b/rev$</TEX> hub loads. Nearly 10 to 40% of hub loads is reduced by appropriately tailoring the fiber orientation angles in the laminae of the composite blade.

Measuring the performance of a novel fluid film bearing supporting a rotor on a stationary shaft, by non-contacting means

A description is given of a multi-body dynamics rig for testing a novel rotor fluid film bearing system. The design included a composite rotor supported on a stationary central shaft, with loading applied by non-contacting electromagnets. The shaft included hydrostatic bearing pockets and continuously adjustable hydrodynamic bearing segments. A technique is described for deriving displacement coefficients for both types of bearing. Observations are given on the use of the rig and test techniques, along with some results, and on implications of the results regarding the bearing system.