טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentMayo Liran
SubjectResearch in Reduction of Vibroacoustic Vibration on a
Payload in an Airborne Body
DepartmentDepartment of Design and Manufacturing Management
Supervisor Professor Haim Abramovich


Abstract

Airborne bodies are exposed to many environmental conditions during their service. The environmental conditions can cause excitation and vibration due to various reasons:

1.      Excitation as a result of aerodynamics of the body - excitation caused by the body's contact with the air (friction). Occurs mainly during free flight and it is transferred to the internal payloads by the supports of the component to the airborne body.

2.      Excitation as a result of the platform that carries the body - a body anchored to the platform experiences vibration coming from the point of connection between them. The excitation is transmitted to the internal payloads by the supports of the component to the airborne body.

3.       Excitation caused by noise in the vicinity of the aircraft - engine noise and pyrotechnic shocks cause pressure waves (sound waves) that advance at the speed of sound towards and within the airborne body and stimulate it.

Various components in the airborne body, mainly electronic boxes and seekers, are subject to various dynamic excitations and are particularly sensitive to environmental conditions. The effect of acoustic pressure waves on mechanical components is large and these pressure waves can cause a great excitation of the components. In addition, the acoustic excitation greatly influences the structure of the airborne body, in the form of fatigue damages and cracks of the structure itself.

In the present research, a method was examined to reduce the influence of vibro-acoustic excitation on the components of the system, in the form of material changes in the -component, in order to help the various components within the airborne body to deal with the environmental conditions and to reduce excitations of this sort. An experiment system was planned to simulate an airborne body (Thin-walled cylinder) with an internal "payload". The internal system consists of an extruded beam with a weight in its tip, harnessed to the cylinder by a "Support, which was the subject of the experiment. In the experiment, mechanical excitation (with a shaker) and acoustic excitation (with a reverberant chamber) were applied on the system. During the tests, the dynamic response of the internal "payload" was tested due to the effect of the material which the support is made of. The support was manufactured from aluminum and magnesium alloys. The purpose was to examine the effect of the damping ratios of the various materials on the dynamic response of the internal system to various excitations .

The results of the experiment show that magnesium is a feasible solution to reduce vibration. But due to the effects of acoustics on the measurements there are some questions to be answered in future studies.

In addition, during the course of the research, additional questions were raised, such as: how to apply the mechanical excitation in conjunction with the acoustic excitation and more. It can be said that the research provided much information on the subject and provides a fair basis for further work on the subject .