An active tendon concept in rotorcraft with variable speed rotors: free vibration perspective

Mechanical Systems and Signal Processing

2019

Theoretical and experimental modal analysis of the system consisting of the Euler-Bernoulli beam axially loaded by a tendon is studied in the paper. The beam-tendon system is modelled using a set of partial differential equations derived by Hamilton's principle and the coupling between the beam and the tendon is ensured by the boundary conditions. Theoretical modal analysis is conducted using a boundary value problem solver and the results are thoroughly experimentally validated using a bench-top experiment. In particular, the effect of the tendon tension on the modal properties of the system is studied. It is found that by increasing the tension, the natural frequencies of the beam decrease while the natural frequencies of the tendon increase. It is also shown that these two sets of modes interact with each other through frequency loci veering. The effect of the tendon mass is also experimentally and numerically studied and it is shown that lighter tendon produces fewer vibration modes in the studied frequency region. Two further numerical studies are conducted to demonstrate the effect of the tendon on the torsional modes of the beam, and to study the structural stability. Overall, an excellent agreement between the numerical and experimental results is obtained, giving the confidence in the derived theoretical model.

Section: Discussionmentioning

confidence: 99%

Theoretical and experimental modal analysis of a beam-tendon system

Mechanical Systems and Signal Processing

2019

“…Moreover, it is believed that the veering, caused by the interaction between the tendon-dominated and beam-dominated modes, can be utilised as a vibration absorber, and hence further enhance the capabilities of an active tendon concept. A preliminary investigation of this possibility has been already conducted in [35], but a more systematic investigation is needed.…”

Section: Discussionmentioning

confidence: 99%

“…Moreover, it might be possible to utilise the veering as an active vibration absorber. This possibility is briefly investigated in [35], but it requires further research.…”

Section: Full Frequency-loading Diagrammentioning

confidence: 99%

Free vibration analysis of a rotating pre-twisted beam subjected to tendon-induced axial loading

Journal of Sound and Vibration

2019

The main objective of this paper is to investigate free vibration of a rotating pre-twisted beam with bendingbending-torsion coupling that is axially loaded by a tendon. The tendon is connected to the tip of the beam, passes through its body, and is fixed and loaded at the axis of rotation. Due to their connection, the motion of the beam influences the motion of the tendon and vice versa. The equations of motion of the beamtendon system are introduced and solved numerically by a combination of a boundary value problem solver and differential quadrature method to obtain the natural frequencies and mode shapes of the system. The numerical implementation is firstly validated against literature for a non-rotating beam-tendon system and a rotating pre-twisted blade. Then, the effect of the tendon on the free vibration of the system is studied for a wide range of loading cases and rotation speeds. From the computed modal characteristics, it is found that the presence of a tendon leads to the frequency shift of beam's natural frequencies as well as frequency loci veering between the beam-dominated and tendon-dominated modes. Both of these effects strongly depend on the beam-tendon rotation speed.

“…and loaded in the same plane as the beam. Unlike in the previous studies [21,22,26,27], the tendon does not coincide with the elastic or mass axis and can be placed in any point of the cross-section as long as it does not collide with the walls of the beam during its motion. The tendon is attached using a tip fixture, characterised by its mass and moment of inertia.…”

Section: Theoretical Modelmentioning

confidence: 98%

“…Therefore, it has been suggested to incorporate a tendon in a rotorcraft blade to introduce a means of controlling its dynamics properties [25]. This was shown [26] as a possible resonance avoidance mechanism which allows rotorcraft to operate with shape adaptive blades or with variable rotor speed, thereby increasing their performance and efficiency. In all these studies, the tendon was attached to the beam's tip so that the place of the attachment coincided with the shear centre of the beam.…”

Section: Introductionmentioning

confidence: 99%

Theoretical and experimental free vibration analysis of a beam-tendon system with an eccentrically placed tendon

2019

Thin-Walled Structures

Theoretical and experimental free vibration analysis of a beam-tendon system is presented in this paper. The system consists of a thin-walled cantilever beam with an open cross-section and a tip mass which is loaded by an eccentrically placed tendon. The novel beam-tendon system is modelled using a set of partial differential equations and numerical free vibration analysis is conducted using a boundary problem solver. The results are thoroughly validated using a bench-top experiment and a high-fidelity finite element model. The effect of the tendon location on the frequency-loading diagrams is systematically investigated for the first time. The results demonstrate that the location of the tendon significantly influences natural frequency shifts caused by the applied axial load and it is observed that some natural frequencies can even increase with the increasing compressive axial loading for certain locations of the tendon. In addition, veering between the beam-dominated and tendon-dominated modes is studied and the structural stability of the system is discussed. The paper concludes with suggestions of practical applications of a beam-tendon system with an eccentrically placed tendon.