Showing papers on "Helicopter rotor published in 2020"

A Two-Stage Synchronous Vibration Control for Magnetically Suspended Rotor System in the Full Speed Range

Abstract: The vibration suppression in the presence of gyroscopic effects is an important issue for safe operations in magnetic bearing levitated varying speed rotor system. This paper proposes a synchronous vibration control method with a two-stage notch filter for the magnetically suspended rotor system with strong gyroscopic effects. First, the dynamics of the magnetically suspended rotor system with synchronous vibrations in the rotational motion is modeled. Then the proposed two-stage notch filter is designed and the solution of the two-stage switching point is derived to distinguish low speed and high speed. Stability analysis is also presented in the low-speed region and the high-speed region, respectively. Finally, simulation results demonstrate that the stability can be guaranteed by adjusting the phase shift angle of the notch filter over the entire speed range. Further experimental results confirm the effectiveness of the proposed suppression method.

Feature extraction method based on NOFRFs and its application in faulty rotor system with slight misalignment

Abstract: Fault features extraction method for slight misalignment of rotor systems is researched in this paper. When a rotor system with faults is excited by harmonic inputs, system response will contain higher harmonic components. Phenomenon of these higher harmonics implies the presence of nonlinear features in a rotor system. When extracting these nonlinear features, traditional methods have certain limitations, and it is easy to ignore weak features of a rotor system. Nonlinear output frequency response functions (NOFRFs) can extract effectively nonlinear features of a rotor system from noise-containing vibration signals and are used in many fault diagnosis fields. However, as for weak damage to structures and in the early stages of a system faults, fault features reflected by high-order NOFRFs are not still obvious enough. Therefore, a new method, named variable weighted contribution rate of NOFRFs, is proposed in this paper. This method enhances the ratio of high-order output frequency response to total output response of a rotor system. Based on this method, a new index MR is proposed to detect the faults of a rotor system. In addition, lumped mass model is used in this paper to simulate misaligned rotor system with slight misalignment, and the sensitivities of the traditional methods and new index for slight misalignment fault features extraction are compared. The results indicate that the new index is more sensitive for the slight misalignment rotor system. Additionally, the rotor system with misalignment fault experiment table is built, and the effectiveness of this new index for detecting the slight misalignment fault of the rotor system is verified.

Wakes of rotorcraft in advancing flight: A large-eddy simulation study

Abstract: We perform the large-eddy simulation of the flow past a helicopter rotor to support the investigation of rotorcraft wake characteristics and decay mechanisms. A hybrid Lagrangian–Eulerian vortex particle–mesh method is employed to simulate the wake development with the blades modeled using immersed lifting lines. The validity of the numerical approach is first evaluated through a comparison of the rotor trim parameters with experimental results. Then, the rotor wake at low, medium, and high advance ratios is simulated up to 30 rotor diameters. The wake generation and roll-up are described (i) qualitatively using rotor polar plots and three-dimensional (3D) vortex dynamics visualizations and (ii) quantitatively using classical integral diagnostics in cross sections. The highly 3D unsteady near wake transitions to a system dominated by two parallel vortices over a distance that depends on the advance ratio. This process is accelerated by the multiple interactions between successive tip vortices, supporting the generation of self-induced turbulence and uncovering a mechanism of vorticity alignment along the streamwise axis. The vortices in the far wake are compared to typical aircraft ones and exhibit less compact cores and faster decaying energy. Finally, we illustrate the loss of time periodicity in the far wake using the power spectral density of the kinetic energy, and the backscattering of energy from high rotor harmonics to lower frequencies, as complementary evidence of the intense vortex interaction activity.

Filter Cross-Feedback Control for Nutation Mode of Asymmetric Rotors With Gyroscopic Effects

Abstract: The nutation mode is an obstacle to the stability improvement of a magnetic-bearing-supported rotor system with significant gyroscopic effects. This article explores a parameter design method of the filter cross feedback for the nutation mode suppression of asymmetric rotor systems supported by active magnetic bearings (AMBs). First, the coupled multi-input multi-output model of the asymmetric AMB rotor system is converted into an equivalent complex single-input single-output model. The equivalent transformation aims at easing the system analysis and extending the classical stability criterion to the complex coefficient frequency domain. Then, the double-frequency bode plot and the Nyquist criterion are used for analyzing the stability of the AMB rotor system and designing the parameters of the filter cross feedback exactly. Simulation results show that the designed filter cross-feedback method has a good performance for suppression of the nutation mode. Finally, the power spectrum level of the nutation component is below $-$ 60 dB after the filter cross-feedback method is implemented in the controller of a large-scale magnetically suspended turbomolecular pump. The experimental results validate the effectiveness of the proposed method.

Reliability Analysis of Aero-Engine Compressor Rotor System Considering Cruise Characteristics

Abstract: This paper develops an improved dynamic reliability model for compressor rotor system, defined as a “unconventional active system” here. First, regarding to the variety of system-component connections, system specific reliability modeling technique is presented, in which the stress and strength are both nonnegative stochastic processes. The new model fully considers the load characteristics of rotor blades, and inherently embodied the effect of the statistical dependence between the failures of the rotor blades. Then, calculated by the new model, the relationship between reliability and time, and that between the hazard rate and time, for a compressor rotor system are discussed, respectively. Comparing to the traditional series system reliability model, the new system reliability model developed in this paper has higher accuracy for compressor rotor system, since the traditional models neglect the difference between compressor rotor system and traditional active system. Moreover, in order to master the cruise characteristics of the aero-plane during reliability analysis of its compressor rotor blade set, a flight cruise is separated into several stages based on the value of Mach number and its change rate, and a subsection solution method is innovatively proposed accordingly. At the end of the paper, a certain cruise of fighter plane is analyzed to verify the accuracy of the new method. The results show that, as to a flight cruise with different stages, the new method is basically reasonable to most of the load histories, especially for the situation with impact loads existing.

Effects of Atmospheric Turbulence Unsteadiness on Ship Airwakes and Helicopter Dynamics

Abstract: In the present work, unsteady effects present in a ship airwake are further analyzed. The effort is performed in the context of simulation of helicopter launch and recovery operations under a reali...

Shrinking Horizon Model Predictive Control Method for Helicopter–Ship Touchdown

Abstract: A model predictive control (MPC) framework with a fixed maneuver horizon and shrinking prediction and control horizons is presented that, at each time step, minimizes the most accurate prediction o...

Suppression of Synchronous Current Using Double Input Improved Adaptive Notch Filter Algorithm

Abstract: In order to suppress the influence of the synchronous vibration generated by the unbalance of magnetically suspended control moment gyro on the attitude control accuracy and stability of the satellite platform, this article first introduces the working principle of the magnetically suspended high-speed rotor system, and also establishes the dynamic model of the magnetically suspended rotor with unbalance mass. At the same time, the main sources of unbalance vibration are also analyzed. Finally, an improved adaptive notch filter based on double input is designed. The filter takes the rotor radial X, Y two-channel displacement sensor signals as inputs, and uses the characteristics orthogonal to each other to simultaneously enter the system. The rotor can be automatically balanced by adjusting the convergence factor and the compensation angle to adaptively suppress the synchronous current in a widely operating speed range. Simulation and experimental results show that the method can effectively eliminate the synchronous current in a widely operating speed range and improve the stability of the system. This research on the microvibration of the rotor is of great significance and application value.

The Sommerfeld effect of second kind: passage through parametric instability in a rotor with non-circular shaft and anisotropic flexible supports

Abstract: A rotor system with asymmetry in its bending flexibility as well as in its support bearings has many stable and unstable speed ranges. The dynamics of such a system is governed by differential equations with time-varying parametric coefficients which lead to parametric instability in certain rotor speed ranges. In this study, an asymmetric rotor shaft having a rotor disc placed firmly on its centre is considered. The rotor shaft is mounted on two bearings at its two ends having stiffness asymmetry. A permanent magnet-type DC motor is used to drive the rotor. When rotor approaches the lower limit of any unstable speed range, the rotor spin speed is captured at that speed with increasing whirl amplitudes and the rotor speed does not respond to an increase in the motor power, unless there is sufficient surplus power to accelerate the rotor through the corresponding unstable speed range. With this surplus power, the escape from lower instability limit speed to a much higher stable speed takes place as a nonlinear jump phenomenon. In certain situations, escape from one unstable speed range may lead to capture at another unstable speed range or simultaneous escape from the next unstable range. This specifically occurs due to the presence of the non-ideal drive and is termed here as the Sommerfeld effect of second kind. Unlike regular Sommerfeld effect (of first kind) where the power scarcity at the resonance is the cause of speed capture; there is, ideally, no need for a residual rotor unbalance in the Sommerfeld effect of second kind. In both the cases of speed capture, the excess motor power is spent to increase the whirl amplitudes. The Sommerfeld effect of the first kind relates to the resonance at the synchronous rotor whirl (critical speeds), whereas that of the second kind relates to instability of the rotor whirl. Due to such nonlinear jumps, some of the speed ranges where the rotor is theoretically stable under ideal or mathematical conditions may not be reached in practice, i.e. with a real drive which is naturally non-ideal. The dynamics of this rotor system is analytically and numerically studied in this article. The numerical simulations are performed with a multi-energy domain bond graph model which guarantees energetic consistency of the model.

Synchronous Vibration Suppression of Magnetically Suspended Rotor System Using Improved Adaptive Frequency Estimation

Abstract: The rotor system of magnetically suspended control moment gyro (MSCMG) inevitably has unbalanced amount due to errors in its materials and processing accuracy. The mass unbalance of the rotor will cause the system to generate synchronous vibration and then transmit it to the spacecraft platform through the base, which will seriously affect the imaging quality. The realization of synchronous vibration suppression depends seriously on the rotor speed signal. When the Hall speed sensor has a large measurement error or fails, it is necessary to adaptively estimate the rotor speed to suppress the unbalance vibration of the rotor system. This paper proposes an improved adaptive frequency estimation (IAFE) method. This algorithm uses the characteristics of the rotor radial displacement sensor signal to adaptively estimate the rotor speed, and then suppress the synchronous current generated by the control system. It maintains the stability of the system by changing the phase shift angle at different frequencies, and the residual displacement stiffness force is also compensated. The simulation results show that the proposed method is easy to be implemented, and it can achieve high-precision suppression of unbalanced vibration.

Effects of Rub-Impact on Vibration Response of a Dual-Rotor System-Theoretical and Experimental Investigation

Abstract: In order to understand the mechanism of fixed-point rub-impact in aero-engine, a dual-rotor system with inter-shaft bearing able to describe the mechanical vibration caused by unbalance and fixed-point rub-impact is developed in this paper. Firstly, a finite element (FE) model of the dual-rotor based on Timoshenko beam element and disk element is proposed, in which the effects of gyroscopic moments, rotary inertias, bending and shear deformations are taken into account. A rub-impact model is developed to derive the rubbing force between the rotor and fixed limiter, in which the softening characteristics of coating painted in casing is fully taken into account. Moreover, the Coulomb model is applied to describe the frictional behaviors. Secondly, the governing equations to describe the motion of the dual-rotor system with rub-impact are solved numerically by the Runge-Kutta method, and the dynamic characteristics are investigated by 3D water-fall plots and frequency spectrum. Combined harmonic frequency, whirling frequency and rotational frequency components of dual rotors are observed. Finally, the experiments of fixed-point rub-impact are performed on a dual-rotor test bench. Good agreement between the theoretical and experimental results shows the accuracy of the dual-rotor FE model and rub-impact model. The results indicate that (1) first backward whirling and forward whirling are excited under the influence of unbalance force; (2) several combination frequency components and second backward whirling and forward whirling frequency components are presented under fixed-point rubbing condition.

Nonlinear vibration analysis of a rotor system with parallel and angular misalignments under uncertainty via a Legendre collocation approach

Abstract: In this paper, the propagation of bounded uncertainties in the dynamic response of a misaligned rotor is investigated using a Legendre collocation based non-intrusive analysis method. A finite element rotor model is used and the parallel and angular misalignments are modelled by additions of stiffness and force terms to the system. A simplex meta-model for the harmonic solutions of the vibration problem is constructed to take into account the uncertainties. The influences of uncertainties in the fault parameters are analysed and the calculation performance of the interval method is validated. Different propagation mechanisms of the uncertainties are observed in the interval responses and discussed in case studies. The results of this study will promote the understandings of the nonlinear vibrations in misaligned rotor systems with interval variables.

Stroboscopic aliasing in long-range interacting quantum systems.

Abstract: We unveil a mechanism for generating oscillations with arbitrary multiplets of the period of a given external drive, in long-range interacting quantum many-particle spin systems. These oscillations break discrete time translation symmetry as in time crystals, but they are understood via two intertwined stroboscopic effects similar to the aliasing resulting from video taping a single fast rotating helicopter blade. The first effect is similar to a single blade appearing as multiple blades due to a frame rate that is in resonance with the frequency of the helicopter blades' rotation; the second is akin to the optical appearance of the helicopter blades moving in reverse direction. Analogously to other dynamically stabilized states in interacting quantum many-body systems, this stroboscopic aliasing is robust to detuning and excursions from a chosen set of driving parameters, and it offers a novel route for engineering dynamical $n$-tuplets in long-range quantum simulators, with potential applications to spin squeezing generation and entangled state preparation.

Innovative Blade Trailing Edge Flap Design Concept using Flexible Torsion Bar and Worm Drive

Abstract: In this paper, a simple but effective trailing edge flap system was proposed. This preliminary concept uses a more practical and stable actuation system which consists of a motor-driven worm gear drive and flexible torsion bar. The flexible torsion bar is designed to be easily twisted while keeping bending rigidity as a sup-port and the worm gear drive not only provides a high torque to overcome aero-dynamic forces on the flap area and the torsional rigidity of the support bar, but also acts as a brake to avoid instability due to the high torsional flexibility of sup-port bar. A preliminary level design study was performed to show the applicability of the new trailing edge flap system for wind turbine rotor blade or helicopter blade.

Experimental Study on the Effect of Different Parameters on Rotor Blade Icing in a Cold Chamber

Abstract: Icing phenomenon is an important problem in helicopter rotor design. Conducting experiments in a cold chamber is one of the main methods used to study the law of rotor icing. The purpose of this paper was to analyze the influence of different parameters on the ice shapes of rotor blade and to obtain the relationship between the ice shapes and the input parameters. The icing experimental platform of rotation blade in a cold chamber was set up, and the rotor icing experiments under various conditions were carried out. The ice shapes on the blade were obtained, and the influence of different icing temperatures, rotation speeds, liquid water content, icing times, number of blades on the rotor, and blade materials on the ice shapes were analyzed. The results showed that the ice thickness on the leading edge increased with the increase of liquid water content, rotation speed, and icing time, and the number and material of blades had little effect on icing. The conclusions of this paper can provide a reference for the rotor numerical simulation and future experimental research.