A New Method of Notching in Vibration Control

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Addis Ababa University


The traditional vibration test methodology of controlling the interface environment only to a motion based specification is often too conservative, inducing potentially excessive vibration responses at hardware resonant frequencies. This over testing problem occurs because the smooth, input acceleration specification used in the test configuration is characteristic of a rigid, infinite impedance equipment mount; and not characteristic of the compliant, finite impedance equipment mount more typical of the service configuration. Recently, the so called Force Limited Vibration (FLV) testing developed at the Jet Propulsion Laboratory offers many opportunities to decrease the over testing problem associated with traditional vibration testing. FLV testing methodology, controls the input acceleration and limits the reaction forces between the test item and the shaker through real-time notching of the input acceleration, is often hard subject to apply the force gauges. This problem has been recognized in this work and the energy limiting vibration test methodology has recently emerged as a viable solution which makes use of stress feedback signal to the vibration control loop using strain gauges that are trouble-free to the functions they are meant to perform. The underlying theoretical basis of the energy limiting vibration testing technique is the strain energy value which is the integration of product of vonmises stress and strain over an element is a parameter prime important since it is related to the total amount of energy transmitted to the test item during the vibration. To illustrate this methodology, a case study of a typical satellite presented to prove the effectiveness. A procedure was proposed to identify the topological location of notch channels or critical locations using FEM results of the base excitation, so as to enable the vibration control mechanism to adjust the power input of shaker table. The base excited dynamic response analysis yielded the percentage reduction of shaker power. The notching of the force limiting and energy limiting vibration testing methods were compared and founded incomparable even though it is acceptable.



Applied Mechanics stream