Search Results

The shape memory phenomena that some materials possess have allowed their use in numerous applications. In the vibration field, we have the control in which the actuator consists of Shape Memory Alloys (SMA). However, the application of these actuators in vibration control in rotors is not very exploited. Thus, in this paper, we present a methodology for vibration control in rotors using a finite element model to compute the complex response of the system when it is subjected to unbalance forces. The vibration control is performed by controlling the stiffness of the bearing involved with springs made of SMA materials.

Vibration and noise signals coming of performing measurements in rotating systems - like reciprocating engines, transmissions, compressors, and pumps, for example - operating in non-stationary condition present some harmonic components that are rotational speed dependent, which are commonly know as orders. It is well known that if one intends to isolate one or some components of these signals, it is not recommended to use the traditional Fast Fourier Transform - if the analysis is in the frequency domain - or a fixed frequency band filter - to study it in the time domain. In these cases, it is important the use algorithms capable of treating those signals properly. This paper deals with the utilization of the Vold-Kalman filter to extract or eliminate a specific order component. This type of filter is able to track a time variant component using a reference signal - usually the angular displacement or velocity of the shaft.

In this paper, the TVDFT Order Tracking technique (Time Variant Discrete Fourier Transform) is used to process complex non-stationary signals, generated by real measured signals. The method is applied in an experimental set-up for several run-ups, in order to identify the forward and backward precession movement in the directional order map. In this map, the negative orders are related to the backward and the positive ones to the forward orbit movement. The directional order maps are obtained for several rotor stations in order to identify the mixed operational modes, i.e., when some stations of the rotor describe their precessional movement in the forward direction while others move in the backward direction simultaneously. The experimental results showed the influence of the spatial distribution of the imbalance in the occurrence of the mixed operational modes.

The quality of the results of any order analysis depends on the accuracy of the tachometer signal used to estimate the instantaneous rotational speed. There are several techniques used to process the tachometer signal. However, in some cases, there are difficulties in measuring this signal due to physical limitations of the equipment under analysis. This paper investigates a methodology to estimate the instantaneous frequency of a nonstationary signal using the Directional Wigner Distribution. Therefore, the variation of the rotational speed of a rotating equipment can be obtained using only the accelerometer signal, eliminating the need of acquiring the tachometer signal.

Improvement of fuel economy is one of the most important development targets of modern passenger car engines. Modern solutions such as Direct Injection, Variable Valve Trains, or Cylinder Deactivation help to obtain this requirement. Each one of these techniques optimize the thermodynamic efficiency of the engine. However, the mechanical structure of combustion engines shows many areas of possible optimization regarding the mechanical efficiency. Engine friction affects the overall fuel consumption, mainly under low speed conditions combined with part load. Low speed/part load conditions are relevant for the real life fuel consumption of an engine, as well as friction improvements have significant effects on the fuel economy. The valve train drive produces the dominant friction portion under these conditions. Hence the friction optimization of this engine subsystem is one of the key issues regarding mechanical efficiency.