In this paper the feasibility of actively suppressing rotor and blade vibration via shaft-based actuation is studied. A mathematical model is derived, taking into account the special dynamical characteristics of coupled rotor-blade systems, such as centrifugal stiffened blades and parametric vibration modes. An investigation of controllability and observability shows that if the blades are properly mistuned, it is possible to suppress shaft as well as blade vibration levels by using only shaft-based actuation and sensing; though, in tuned bladed systems, shaft as well as blade actuation and sensing are required. In order to cope with the time-variant dynamics of the coupled rotor-blade system, a periodic time-variant modal controller is designed, implemented, and experimentally tested. A test rig built by four flexible blades is specially designed for this purpose. The rig is equipped with six electromagnetic actuators and different types of sensors (eddy-current displacement transducers, acceleration transducers, and strain gages) with the aim of monitoring and controlling shaft and blade vibration levels. Two different actively controlled rotor-blade system configurations are considered in the present study: (i) a tuned bladed rotor, controlled with help of actuators attached to the rotating blades and shaft-based actuators; (ii) a deliberately mistuned bladed rotor controlled only via shaft-based actuation. Experimental tests are carried out for both configurations. Some experimental problems regarding control implementation are identified and discussed, especially when the controller order and the number of actuators in the centralized control scheme become too high; though, for the mistuned bladed rotor controlled by using only shaft-based actuation, the controller works well.
Accurate acoustic models of small devices with cavities and narrow slits and ducts should include the so-called boundary layer attenuation caused by thermal conduction and viscosity. The purpose of this paper is to present and compare different methods for including these loss mechanisms in analytical and numerical models. Two test cases with circular geometry have been used as references and are investigated both through measurements and the different models. Four simulation methods are compared. The transmission line model is an analytical model which can be modified to include loss. Additionally, three numerical models have been tested. Two different implementations of the so-called Full Navier-Stokes model, one using the commercial package COMSOL Multiphysics, the other using Boundary Element code specifically aimed at the test case, are considered. The third numerical method, the so-called Low reduced frequency model, is evaluated using the commercial package ACTRAN.
This is the first paper in a two-part study on active rotor-blade vibration control using electro-magnetic actuation. Emphasis is focused on theoretical aspects of implementing active control into coupled rotor-blade systems, more precisely, into systems where rotor lateral motion is coupled to blades flexible motion. The theoretical investigation includes controllability and observability analyses of such a system in order to determine optimal actuator and sensor placement. An analysis methodology based on modal analysis in time-variant systems, due to the periodic time-variant nature of this kind of system, is presented. The method takes into account the strong vibration coupling which has a significant effect on the controllability and observability of bladed rotor systems. The analyses show that, for tuned bladed rotors, actuators will have to be located within the blades in order to make all vibration modes controllable. However, if the system is deliberately mistuned, rotor and blade vibrations can be controlled using shaft-based actuation and sensing only. Moreover, a controller design procedure for obtaining active periodic time-variant modal controllers, capable to cope with the time-periodicity of the system, is presented. Controllers are designed for a tuned as well as a deliberately mistuned system. The tuned system is controlled using both blade and shaft actuators while the mistuned system is controlled using only shaft actuation. Numerical simulations are provided to show the efficiency of the designed controllers.
This is the second paper in a two-part study on active rotor-blade vibration control using electro-magnetic actuation. This part is focused on experimental aspects of implementing active control into coupled rotor-blade systems. A test rig, equipped with electro-magnetic actuators and various sensors to monitor the system vibration levels, is specially designed. The aim of the rig is to demonstrate the feasibility of controlling rotor and blade vibrations using a modal control scheme capable to handle the time-periodicity of this kind of system. Two different active controlled rotor-blade systems are considered in the present study: (a) a tuned bladed rotor, controlled with help of actuators attached to the rotating blades; (b) a deliberately mistuned bladed rotor controlled only by shaft based actuation. Experimental tests are carried out for both systems. Some experimental problems regarding control implementation are identified and discussed especially when the controller order and the number of actuators in the centralized control scheme become too high. For the blade mistuned system, controlled by using only rotor/hub based actuation, the controller works well. Despite of implementation difficulties of the modal control scheme due to high sensitivity to model imperfections, it can be concluded that the periodic modal control methodology applied to controller design works well and can become a very useful and powerful tool for designing mechatronic machine elements.
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