https://web.iitd.ac.in/~achawla/PDF%20Files/Transient%20response%20and%20breathing%20behaviour%20of%20a%20cracked.pdf

Transient response and breathing behaviour of a cracked Jeffcott rotor

Swept sine testing of rotor-bearing system for damping estimation

This paper focuses on the nonlinear dynamic and bifurcation characteristics of an aircraft rotor system affected by the maneuvering flight of the aircraft. The equations of motion of the system are formulated with the consideration of the nonlinear supports of Duffing type and the sine maneuver load of a proposed maneuvering flight model. By utilizing the multiple scales method to solve the motion equations analytically, the bifurcation equations are obtained. Accordingly, the response and the bifurcation characteristics of the system are analyzed respectively. Basically, the increase of the maneuver load may increase the formant frequency as well as the primary resonance frequencies. Through numerical simulations, four different types of response characteristics of the system during the maneuvering flight are found, which are compared with the theoretical results, and it shows good qualitative agreements between them. Furthermore, the maneuver load can make an apparent effect on the bifurcation. The results in this paper will provide a better understanding for the effect of aircraft maneuvering flight on the dynamics and bifurcations of the rotor system.

Nonlinear response and bifurcation analysis of a Duffing type rotor model under sine maneuver load

The three main noise sources in modern cars and trucks are tyre/road interaction, wind turbulence, and the power plant. The power unit noise is composed of contributions from the fan, engine, exhaust, and transmission. In addition, the engine noise contains contributions from the injection system, intake, and cylinder block. Noise is of course a problem both inside the passenger compartments (interior noise) of vehicles and in residential areas near to the highway on which the vehicles are traveling (exterior noise). In most modern automobiles, the engine and exhaust noise have been sufficiently suppressed so that they are no longer the dominant interior or exterior noise sources. On heavy trucks, the engine is normally a diesel, and the suppression of its noise is more difficult. With vehicle noise, regulations are mostly concerned with exterior noise of vehicles, and this paper will consider mostly the exterior noise. Of course, if the exterior noise is reduced, the interior noise is normally reduced as well, although the relationship may not be quite linear. With modern well designed automobiles, the exterior noise is dominated by tyre noise at almost all speeds, even under accelerating conditions, except for acceleration in the first and second gears. With trucks, however, at speeds up to about 70 km/h, engine and exhaust noise is dominant under accelerating conditions. But above this speed, tyre noise becomes equally as important as engine, exhaust, and other power unit related noise sources, particularly as far as the exterior noise is concerned. This fact has been observed experimentally, and it has been found that similar trends exist for the exterior noise of a wide variety of manufactured vehicles and that the exterior noise of automobiles is significantly less than that of heavy trucks by almost 15 dB at low speed and by almost 10 dB at medium to high speed. One can conclude from the previous discussion that much of the exterior noise emitted from modern cars and trucks, particularly at medium to high speeds, is caused by tyre/road interaction noise. Of course, the frequency content of noise as well as its magnitude is very important. It has been observed that for automobiles travelling at medium to high speeds, the A-weighted noise peaks at about 1000 Hz, while for light and heavy trucks, the annoying noise peaks at a frequency closer to 1200 to 1600 Hz. In addition, it has been shown that the A-weighted exterior sound levels emitted by passenger cars and light and heavy trucks has not changed very much over time. This is probably because the power of automobiles has increased in many countries, particularly in the USA, and it is has been

/pdf/measurements-of-tyre-road-noise-and-of-acoustical-properties-4dfitvo04v.pdf

Measurements of Tyre/Road Noise and of Acoustical Properties of Porous Road Surfaces

Interest in the development of improved composite materials has greatly increased in recent years due to their high energy dissipation characteristics and high stiffness-to-weight ratios. They are used in a variety of highly demanding structural applications, including aircraft, submarines, and military vehicles. There are numerous types of composites currently available, including carbon fibre, metal matrix, and ceramic matrix composites. Of particular interest in the current work is a specific variation of composite construction called “sandwich composites” or “sandwich panels.” The term “sandwich panel” refers to a structure consisting of two thin faces bonded to a thick lightweight core. Photographs of some typical sandwich composite structures, with a honeycomb core, are shown on Fig. 1. The faces are typically of aluminum or some composite laminate, and the core could be a lightweight foam or a honeycomb structure. 1.1. Mathematical Model

/pdf/parameter-characterisation-of-the-bouc-wen-mechanical-3scshjl6hf.pdf

Parameter Characterisation of the Bouc/Wen Mechanical Hysteresis Model for Sandwich Composite Materials using Real Coded Genetic Algorithms

Influence of Acceleration on the Critical Speed of a Jeffcott Rotor

A small, lightly damped rotor (ζ=0.0088) was experimentally tested for a variety of acceleration and deceleration rates. In each case, the amplitude response was plotted as a function of operating speed, with the acceleration rate considered. In each case the results are compared with theoretical predictions. The results agree within 6% at the peak response. The results of the analysis indicate that for high acceleration rates the critical amplitude response may be reduced by a factor of four or more. The frequency of the effective critical speed may be shifted by up to 20%. Furthermore, a beating frequency was observed in the amplitude data after the rotor had passed through the critical speed. This phenomenon is shown to be the vector sum of a synchronous component of amplitude and a nonsynchronous transient component (at the critical speed). The transient nonsynchronous component is shown explicitly via electronic band-pass filtering, as is the forced response component. Finally, spectral analyses were performed over a range of operating speeds, yielding waterfall diagrams and further verification of the existence of the two components.

H. L. Hassenpflug

Papers

Influence of Acceleration on the Critical Speed of a Jeffcott Rotor

Experimental study of the critical speed response, of a jeffcott rotor with acceleration